Inside the warehouse in Israel where the US is overseeing Trump’s peace plan

Two hundred U.S. troops working with Israel’s military and other partners have scrambled over the past week to build out a new Civil-Military Coordination Center. It will monitor the fragile cease-fire between Israel and Hamas and coordinate the flow of aid and security assistance to Gaza, which lies roughly 20 miles away.

Like the plan itself—which freed the remaining live hostages in Gaza nearly two weeks ago and is now moving on to the more difficult task of creating alternatives to Hamas to administer and secure the enclave—the center is a work in progress.

Dozens of whiteboards partition the vast cement hall, flanked by large displays inscribed with the 20 points of Trump’s Gaza peace plan. The floor of the hall, which is covered with new artificial turf, bustles with soldiers and civilian staff weaving through black panels as a loudspeaker reminds them to not smoke inside.

A makeshift command center projects maps and updates from social media and news reports onto the walls. They also display a message in green letters:

“A new and beautiful day is rising. And now the rebuilding begins. —President Donald J. Trump."

Trump and his envoys pushed the plan into existence with an unorthodox approach: Declare victory then work out the details later. The optimism overcame the parties’ reservations with the plan to free the hostages and brought the first sustained break in the fighting in seven months.

The administration kept up the broadly positive tone this week, even as it sent a string of heavy hitters to Israel to keep the process on track after a string of skirmishes between the combatants last weekend. Top Trump emissaries—including Secretary of State Marco Rubio, Vice President JD Vance, special envoy Steve Witkoff, and Trump son-in-law Jared Kushner—have cycled in and out of Israel in recent days.

Rubio, the latest administration official to arrive, said Friday that the work being done in this warehouse in southern Israel is the “key to holding it all together."

⁠“There is no Plan B," he said after he toured the site with military officials and greeted troops. “This is the best plan. It’s the only plan."

U.S. officials say the hub is a tangible symbol of Washington’s commitment to the Gaza peace deal, which hangs on Trump’s guarantee that Israel won’t resume the war as long as Hamas adheres to the deal’s terms.

It also is a way to keep close watch as Israeli Prime Minister Benjamin Netanyahu navigates domestic pressure from members of his coalition who oppose ending the fight against Hamas, as well as to coordinate with a roster of uneasy regional partners.

Witkoff and Kushner delivered a strong message to Netanyahu in a meeting Monday that Israel must avoid escalation by ensuring responses to any alleged cease-fire violations by Hamas are proportional. Trump has also repeatedly warned Hamas to stop violating the agreement or risk being wiped out.

Military officers from partner countries milled about the new center in small clusters Friday, the flags on their sleeves—including those of Germany, France, Greece, Cyprus, the U.K., Australia and Canada—meant to underscore the international effort to keep the Gaza cease-fire from unraveling. U.S. troops from the Army, Marines and Space Force are represented.

Israeli media has remarked on the sudden influx of American soldiers wandering the streets and ordering restaurant deliveries.

The State Department is dispatching more diplomats to aid the effort. It said Friday that Steven Fagin, the U.S. ambassador to Yemen, will serve as the civilian lead at the center.

While U.S. officials have emphasized there will be no American soldiers on the ground in Gaza, it is assembling an international stabilization force of partner countries. Asked about one of the news headlines projected on the screen behind him reading “U.S. accepted Israel’s veto of Turkish soldiers for ISF," Rubio said Israel will have to be comfortable with composition of the so-called international stabilization force as it is assembled.

While U.S. officials are discussing the makeup of the force with multiple countries, including Egypt, Turkey, the United Arab Emirates, Indonesia, and Azerbaijan, Rubio stressed that basic questions are still being worked out. This includes what their mandate will be, the command structure, legal questions, how it will be paid for and the rules of engagement.

“There’s a lot to work through," Rubio said. “That’s why there’s all these people working in this building."

Part of the monitoring involves following public information on developments in Gaza. On Friday, the roundup included updates on the return of the bodies of hostages and the availability of food in the enclave.

U.S. officials say the coordination effort is bringing together a mix of international and humanitarian organizations, including the World Food Program, to deliver aid. The day before Rubio’s visit, the center set up a working group on dual-use items to improve access to items needed for the winter and healthcare.

The efforts, which are being overseen by Lt. Gen. Patrick Frank, the commander of the U.S. Army Central Command, are still in the early stages. Before Trump announced the deal on Oct. 8, U.S. Central Command chief Adm. Brad Cooper met with Witkoff and Kushner in Egypt and assured them he could have a command center operational within 2½ weeks, a senior administration official said.

“We’ve made more progress in 13 days than anyone thought possible," Rubio said. “We have to make it work. There is no other alternative."

Write to Vera Bergengruen at vera.bergengruen@wsj.com