The Biden administration is scrambling to finalize essential components of its plan to install a floating pier off the Gaza coast for processing food deliveries and other desperately needed humanitarian aid, as famine looms and some U.S. officials doubt whether the military operation is even necessary.

Four Army ships, deployed from southeastern Virginia in mid-March, are due to arrive in the eastern Mediterranean within days. But evolving conditions amid the war have cast new uncertainty over how the effort will play out.

Among the challenges is the precarious security situation in the region, with Iran’s pledge to retaliate for Israel’s deadly strike on a diplomatic compound in Syria raising fears that deployed American personnel face heightened risk. U.S. officials have denied that Washington was involved in the attack, but Tehran maintains that as Israel’s principal supporter, the United States “must be held accountable.”

Another variable is Israel’s recent attack on a World Central Kitchen humanitarian convoy, which killed seven aid workers. While Israel has accepted blame for the strike and said the workers should not have been targeted, the tragedy has complicated U.S. efforts to secure an arrangement for distributing the estimated 2 million meals to be offloaded from the pier daily.

Officials say there also is a lack of clarity about how quickly Israel may follow through on its promise, announced Thursday under pressure from the Biden administration, to open an Israeli port and an additional border crossing to northern Gaza so more aid can get in.

One U.S. official, who like some others spoke on the condition of anonymity to be candid about the administration’s internal deliberations, summarized the predicament this way: “We’re building the plane as we fly it.”

A senior U.S. defense official cautioned that it is too early to speculate whether, ultimately, the pier may not be used, but acknowledged the plan for food distribution remains unsettled. The security plan for the pier, however, has been reached in principle, this official said, with Israeli forces assuring U.S. counterparts they will provide significant protection.

Another defense official said the pier operation is proceeding, at least for now, but questioned whether initial forecasts will hold. After the plan was announced by President Biden during his State of the Union address in March, the Pentagon suggested the pier could be in use for several months. While some officials said that remains the expectation, that timeline may no longer be necessary if other means of aid delivery become available, the defense official said.

Another senior U.S. official disagreed, saying the pier “absolutely” has utility still.

“To get to the order of magnitude of aid that we think is needed, it will require an all-hands-on-deck approach,” this person said. “So we will need not only the ground routes, but also the pier for some duration of time.”

The Biden administration, facing strident criticism over its unflinching support for Israel, has intensified its pressure on Israeli leaders to not only protect civilians in their military campaign but to dramatically increase the amount of food allowed into Gaza. A failure to heed those demands, the White House warned Thursday, could force a change in U.S. policy toward the war.

The humanitarian crisis in Gaza has grown increasingly dire, with people facing extreme hunger and the World Health Organization declaring that parts of the Palestinian enclave could spiral into full-blown famine by May. The classification means that many people have almost no food, bringing about starvation and death.

Officials have said that approximately 1,000 U.S. personnel would build the floating pier and an 1,800-foot two-lane causeway connecting it to a beachhead secured by the Israel Defense Forces. No American service members are expected to go ashore, but they will probably be on the causeway, putting them within range of militants’ rockets and other forms of attack. Operations are expected to begin about May 1.

For the last month, the U.S. Agency for International Development has discussed with aid organizations how the pier could be used, what security it will have and how the operation might complement broader humanitarian efforts in Gaza, another U.S. official said. But those talks have been complicated by the World Central Kitchen tragedy on April 1, which occurred as the charity’s aid workers were delivering food.

About 200 aid workers have been killed in the West Bank and Gaza since the war began in October, according to the United Nations. The strike on World Central Kitchen was especially jarring because the aid workers had coordinated their route with the Israeli military in advance.

“People are really scared now,” the official said, adding that the heads of major humanitarian organizations have relayed to the U.S. government deep concern that Gaza is not suitably safe enough to deploy their staffs.

Israeli officials have called the strike a case of mistaken identity, announcing Friday the removal of the commanders involved and plans to examine their targeting processes to avoid future mistakes. Israel also disclosed Thursday that it would open the Erez border crossing into northern Gaza and the Israeli port of Ashdod, about 20 miles away, potentially boosting the volume of aid let into Gaza significantly.

U.S. officials welcomed the decision, but have taken a wait-and-see approach to whether Israel’s promises are fulfilled. The Israeli Embassy in Washington could not be reached for comment.

A senior administration official said the United States wants to build redundancy into the aid system so that if one port of entry to Gaza is cut off, required supplies can still flow in elsewhere.

“Anything additional that the pier can provide is still much needed,” this person said.

The United Nations is seen as the “primary recipient” and distributor of aid coming off the pier, the senior administration official said, adding that other groups will be welcome to use the pier to bring in their own food but that Israel must regain trust with those organizations after the World Central Kitchen attack.

“There’s no doubt,” the official said, “that the strike … has a chilling effect.”