President Trump’s declaration of “total victory” in Iran left some close allies and several senior aides worried Wednesday that he’s overstating what is a fragile cease-fire with Tehran, which remains capable of blocking ships in the Strait of Hormuz and attacking U.S. forces in the region.

The president has been advised on the risks that could cause the cease-fire to crater and warned that Iran still retains dangerous military capabilities, according to multiple officials.

More than half of Iran’s missile launchers have been destroyed, but a substantial number remain mostly buried deep underground, according to another U.S. official. The Islamic Revolutionary Guard Corps also retains dozens of small boats that can threaten ships in the Strait of Hormuz, the official said, even as strikes have sunk more than 90% of Iran’s regular Navy.

So far, those warnings haven’t tempered the administration’s insistence that it has the upper hand ahead of talks, with White House press secretary Karoline Leavitt at a press conference calling the five-week operation a “military triumph.”

Leavitt told reporters on Wednesday that Iran’s ability to build ballistic missiles and long-range drones had been set back by years, its naval mines mostly destroyed and its air forces “operationally irrelevant.”

In a separate press conference, Defense Secretary Pete Hegseth said the U.S. military achieved “every single objective, on plan, on schedule, exactly as laid out from day one.”

Officials and military experts say Iran’s military and nuclear capabilities are indeed battered. But, they noted, Tehran still has significant capability.

“It’s a variant of the “d” word,” said Behnam Ben Taleblu, senior director of the Iran program at the Foundation for Defense of Democracies. “Iran has certainly been defanged, the regime’s capabilities have been degraded, but there’s a smaller group of things that have been fully destroyed.”

White House spokeswoman Anna Kelly said: “Iran’s ballistic missiles are destroyed, their production facilities are demolished, their navy is underwater, their proxies are weakened, and their dreams of possessing a nuclear weapon are gone.”

“Now, the administration is engaging in diplomatic discussions because the President was able to exert maximum leverage over the Iranian regime, and he is optimistic that this will lead to long-term peace in the region,” she added.

Among the concerns by aides is that Iran was unlikely to reopen the Strait of Hormuz without significant concessions, which Trump was unlikely to grant. That gridlock could result in a resumption in fighting, they said.

On Wednesday, Iran told mediators it would limit the number of ships crossing the Strait of Hormuz to around a dozen a day and charge tolls. The Iranian navy also told ships anchored nearby that they still needed Iran’s permission to cross the strait. “If any vessel tries to transit without permission, [it] will be destroyed,” according to a recording reviewed by The Wall Street Journal.

There were also questions about how Iran might respond to Israeli airstrikes in Lebanon. Israel struck Hezbollah targets on Wednesday, killing dozens of people and injuring hundreds more, according to the country’s Health Ministry.

While the American and Israeli campaign has devastated Iran’s conventional military, Tehran still retains the ability to threaten its neighbors with a depleted arsenal of missiles and drones. Hours after the cease-fire began, Gulf partners said they had intercepted Iranian projectiles.

“My number one concern right now is to see over the next four to six weeks whether we lied to ourselves because we lost our nerve, or whether we got a real agreement with real teeth that involves real change,” said Newt Gingrich, a former House speaker who is close to Trump.

Gen. Dan Caine, chairman of the Joint Chiefs of Staff, said the strikes destroyed roughly 80% of Iran’s air defenses, more than 1,500 targets, as well as more than 450 ballistic missile storage facilities and 800 one-way attack drone storage facilities. The operation has also decimated Iran’s defense industrial base, Caine said, including shattering more than 80% of its missile factories.

Uranium may be the paramount issue. Iran has insisted that it has no plan to build a nuclear weapon, but one of its conditions for ending the conflict is the U.S. accepting Iran’s right to enrich uranium. Iran has provided no indication in its public statement that it is prepared to turn over its highly enriched uranium, though Leavitt said Wednesday Iran privately signaled its intention to relinquish control of the material.

Before the war, Iran wasn’t enriching the uranium, Secretary of State Marco Rubio has acknowledged. But a longstanding concern among Western nations before the war is that Iran had been edging close to the nuclear threshold, giving it the option of sprinting toward a bomb.

Tehran still has stores of highly enriched uranium buried beneath its Isfahan facility and likely at Natanz, according to the International Atomic Energy Agency. The two sites were targeted by U.S. airstrikes last year. If recovered and enriched further, the uranium could provide Iran with nuclear material it needs for a crude bomb or warhead.

Caine told reporters on Wednesday that nearly 80% of Iran’s nuclear industrial base had been hit during the operation. That further degrades its ability to produce a nuclear weapon but leaving 20% available for Iran to use.

In a social-media post, Sen. Lindsey Graham (R., S.C.), a close ally of Trump, said the unrecovered material remained a major concern.

“I want to reaffirm that from my point of view, every ounce of the approximately 900 lbs. of highly enriched uranium has to be controlled by the U.S. and removed from Iran to prevent them in the future from having a dirty bomb or returning to the enrichment business – the Libyan model, for lack of a better phrase,” Graham wrote.

Hegseth said the administration is maintaining the option to seize Iran’s uranium if Tehran doesn’t agree to hand it over. That would be a challenging and potentially risky military operation that Trump has nonetheless discussed with top aides.

“We’re watching it,” Hegseth said. “We know what they have, and they will give it up, and we’ll get it, and we’ll take it if we have to. We can do it by any means necessary.”

Write to Lara Seligman at lara.seligman@wsj.com, Alexander Ward at alex.ward@wsj.com and Michael R. Gordon at michael.gordon@wsj.com

President Trump’s declaration of “total victory” in Iran left some close allies and several senior aides worried Wednesday that he’s overstating what is a fragile cease-fire with Tehran, which remains capable of blocking ships in the Strait of Hormuz and attacking U.S. forces in the region.

The president has been advised on the risks that could cause the cease-fire to crater and warned that Iran still retains dangerous military capabilities, according to multiple officials.

More than half of Iran’s missile launchers have been destroyed, but a substantial number remain mostly buried deep underground, according to another U.S. official. The Islamic Revolutionary Guard Corps also retains dozens of small boats that can threaten ships in the Strait of Hormuz, the official said, even as strikes have sunk more than 90% of Iran’s regular Navy.

So far, those warnings haven’t tempered the administration’s insistence that it has the upper hand ahead of talks, with White House press secretary Karoline Leavitt at a press conference calling the five-week operation a “military triumph.”

Leavitt told reporters on Wednesday that Iran’s ability to build ballistic missiles and long-range drones had been set back by years, its naval mines mostly destroyed and its air forces “operationally irrelevant.”

In a separate press conference, Defense Secretary Pete Hegseth said the U.S. military achieved “every single objective, on plan, on schedule, exactly as laid out from day one.”

Officials and military experts say Iran’s military and nuclear capabilities are indeed battered. But, they noted, Tehran still has significant capability.

“It’s a variant of the “d” word,” said Behnam Ben Taleblu, senior director of the Iran program at the Foundation for Defense of Democracies. “Iran has certainly been defanged, the regime’s capabilities have been degraded, but there’s a smaller group of things that have been fully destroyed.”

White House spokeswoman Anna Kelly said: “Iran’s ballistic missiles are destroyed, their production facilities are demolished, their navy is underwater, their proxies are weakened, and their dreams of possessing a nuclear weapon are gone.”

“Now, the administration is engaging in diplomatic discussions because the President was able to exert maximum leverage over the Iranian regime, and he is optimistic that this will lead to long-term peace in the region,” she added.

Among the concerns by aides is that Iran was unlikely to reopen the Strait of Hormuz without significant concessions, which Trump was unlikely to grant. That gridlock could result in a resumption in fighting, they said.

On Wednesday, Iran told mediators it would limit the number of ships crossing the Strait of Hormuz to around a dozen a day and charge tolls. The Iranian navy also told ships anchored nearby that they still needed Iran’s permission to cross the strait. “If any vessel tries to transit without permission, [it] will be destroyed,” according to a recording reviewed by The Wall Street Journal.

There were also questions about how Iran might respond to Israeli airstrikes in Lebanon. Israel struck Hezbollah targets on Wednesday, killing dozens of people and injuring hundreds more, according to the country’s Health Ministry.

While the American and Israeli campaign has devastated Iran’s conventional military, Tehran still retains the ability to threaten its neighbors with a depleted arsenal of missiles and drones. Hours after the cease-fire began, Gulf partners said they had intercepted Iranian projectiles.

“My number one concern right now is to see over the next four to six weeks whether we lied to ourselves because we lost our nerve, or whether we got a real agreement with real teeth that involves real change,” said Newt Gingrich, a former House speaker who is close to Trump.

Gen. Dan Caine, chairman of the Joint Chiefs of Staff, said the strikes destroyed roughly 80% of Iran’s air defenses, more than 1,500 targets, as well as more than 450 ballistic missile storage facilities and 800 one-way attack drone storage facilities. The operation has also decimated Iran’s defense industrial base, Caine said, including shattering more than 80% of its missile factories.

Uranium may be the paramount issue. Iran has insisted that it has no plan to build a nuclear weapon, but one of its conditions for ending the conflict is the U.S. accepting Iran’s right to enrich uranium. Iran has provided no indication in its public statement that it is prepared to turn over its highly enriched uranium, though Leavitt said Wednesday Iran privately signaled its intention to relinquish control of the material.

Before the war, Iran wasn’t enriching the uranium, Secretary of State Marco Rubio has acknowledged. But a longstanding concern among Western nations before the war is that Iran had been edging close to the nuclear threshold, giving it the option of sprinting toward a bomb.

Tehran still has stores of highly enriched uranium buried beneath its Isfahan facility and likely at Natanz, according to the International Atomic Energy Agency. The two sites were targeted by U.S. airstrikes last year. If recovered and enriched further, the uranium could provide Iran with nuclear material it needs for a crude bomb or warhead.

Caine told reporters on Wednesday that nearly 80% of Iran’s nuclear industrial base had been hit during the operation. That further degrades its ability to produce a nuclear weapon but leaving 20% available for Iran to use.

In a social-media post, Sen. Lindsey Graham (R., S.C.), a close ally of Trump, said the unrecovered material remained a major concern.

“I want to reaffirm that from my point of view, every ounce of the approximately 900 lbs. of highly enriched uranium has to be controlled by the U.S. and removed from Iran to prevent them in the future from having a dirty bomb or returning to the enrichment business – the Libyan model, for lack of a better phrase,” Graham wrote.

Hegseth said the administration is maintaining the option to seize Iran’s uranium if Tehran doesn’t agree to hand it over. That would be a challenging and potentially risky military operation that Trump has nonetheless discussed with top aides.

“We’re watching it,” Hegseth said. “We know what they have, and they will give it up, and we’ll get it, and we’ll take it if we have to. We can do it by any means necessary.”

Write to Lara Seligman at lara.seligman@wsj.com, Alexander Ward at alex.ward@wsj.com and Michael R. Gordon at michael.gordon@wsj.com