Iran would need to master significant technological challenges before it could field an intercontinental ballistic missile capable of striking the U.S. homeland, according to U.S. intelligence estimates and experts outside government.
The assessment raises questions about the Trump administration’s rationale for urgent military action against Iran, which looks increasingly likely barring a major diplomatic breakthrough.
President Trump contended in his State of the Union speech on Tuesday that Iran was working on missiles that “will soon reach” the U.S.
Experts say the formidable technical hurdles facing such Iranian ambitions give the two sides time to discuss a potential agreement to curb Tehran’s missile development. The Trump administration has highlighted the missile question in recent days, along with its longstanding insistence that Iran shut the door on uranium enrichment.
A huge complication is the fact that Iran doesn’t acknowledge pursuing an ICBM and has shown no flexibility, at least in public, about giving up its short-range and medium-range missile arsenal or limiting missile production.
Iranian Foreign Minister Abbas Araghchi said in an interview with Indian TV on Wednesday that Tehran has “deliberately limited” its ballistic missiles to a range of no more than 2,000 kilometers (1,243 miles) and has maintained its missile arsenal purely for deterrence.
U.S. Secretary of State Marco Rubio rejected that stance that same day, saying Tehran was “certainly trying to achieve intercontinental ballistic missiles” and was “headed in the pathway to one day being able to develop weapons that can reach the continental U.S.”
To build effective ICBMs, which soar out of the atmosphere and into space, Iran would have to overcome hurdles including developing a re-entry vehicle with heat shielding that can survive a fiery descent into the atmosphere, and a guidance system to keep the missile on target.
Trump administration officials haven’t said if they plan to declassify intelligence that suggests Iran is accelerating the development of an effective ICBM. The White House didn’t immediately respond to a request for comment.
The Defense Intelligence Agency projected in May that Iran could deploy as many as 60 ocean-spanning missiles by 2035, if it decided to adapt a system it has been developing for putting satellites into low-Earth orbit for ICBMs instead.
U.S. officials say Iran’s space launch program serves as a cover for developing an ICBM as much of the technology overlaps. Since the U.S. struck Iran’s three Iranian nuclear sites last summer, experts say, Iran has conducted tests of a space launch vehicle, one of which appears to have malfunctioned.
To make missiles nuclear-capable, Iran would also need to develop an atomic warhead small enough to fit in such a re-entry vehicle. That would take significantly more time than building a bulky, crude nuclear device in a monthslong crash program, experts say.
A nuclear weapon would also require that Iran enrich uranium to weapons grade, which Rubio confirmed Wednesday that Iran isn’t doing.
“Iran would need to increase the range of its missiles, build a nose cone that could go into space and survive re-entry into the Earth’s atmosphere, and develop a guidance system that would prevent the missiles from wobbling and keep it on track to hit its target,” said Matthew Kroenig, a former Pentagon official who was an adviser to Rubio’s 2016 presidential campaign. “These are serious obstacles, but they are within Iran’s reach over time.”
Some analysts are more doubtful of Iran’s capabilities.
“There’s a huge gap, I think, between where they are now and their ability to have anything that reaches the United States,” said Rosemary Kelanic of Defense Priorities, a group that is skeptical of U.S. military intervention abroad.
Iran has long relied on short- and medium-range ballistic missiles to compensate for the weakness of its air force. Its arsenal includes missiles that can reach U.S. bases in the Middle East as well as southern Europe.
Concern that Iranian missiles might be used to target Europe already has led the U.S. to place missile defense systems in Romania and Poland that have been adapted from the Aegis naval antimissile system. Though Russia has complained about those European-based antimissile systems, they were developed and deployed to counter Tehran.
Iran isn’t the only Middle East nation that has a ballistic missile arsenal. Saudi Arabia acquired intermediate-range ballistic missiles from China in the 1980s. Israel also has ballistic missiles, including an air-launched type, which it used in September in an unsuccessful attempt to kill top Hamas leaders meeting in Qatar.
The size of Iran’s ballistic missile force has stirred fears that it could once again fire the weapons to try to overwhelm Israel’s antimissile defenses and target American troops and Arab allies in the region.
Iran fired more than 500 ballistic missiles during its 12-day war with Israel last year. After the U.S. struck three Iranian nuclear sites with 14 massive bombs, Iran fired 14 missiles at the Al Udeid air base in Qatar, one of which eluded the U.S. and Qatari Patriot air defenses and struck the base. No damage was caused.
Iran’s ability to threaten Israel and Gulf states with conventionally armed missiles and drones has emerged as a major danger even as its nuclear program appears largely stalled.
With U.S. and Iranian negotiators still far apart, some Middle Eastern countries have urged that talks focus solely on the nuclear issues and defer the U.S. demands on Iran’s missile force for a subsequent round of negotiations that might include other states in the region.
So far, the Trump administration has given no indication it is prepared to put the missile issue on the back burner. One concern of U.S. officials is that if the question isn’t tackled when the U.S. has amassed a large force in the region, there is little chance Iran will compromise.
“Iran refuses, refuses to talk about ballistic missiles to us or to anyone, and that’s a big problem,” Rubio said.
Write to Michael R. Gordon at michael.gordon@wsj.com, Lara Seligman at lara.seligman@wsj.com and Robbie Gramer at robbie.gramer@wsj.com