WASHINGTON — The U.S.-built pier to bring food to Gaza is facing one of its most serious challenges yet — its humanitarian partner is deciding if it can safely and ethically keep delivering supplies arriving by the U.S. sea route to starving Palestinians.

The United Nations, the player with the widest reach delivering aid within Gaza, has paused its work with the pier after a June 8 operation by Israeli security forces that rescued four hostages and killed more than 270 Palestinians. Adding to the troubles, two U.S. officials said Friday that the pier would be detached again because of rough seas to prevent it from breaking apart as it did in bad weather last month.

Rushing out a mortally wounded Israeli commando after the raid, Israeli rescuers opted against returning the way they came, across a land border, Rear Adm. Daniel Hagari, an Israeli military spokesman, told reporters. Instead, they sped toward the beach and the site of the U.S. aid hub on Gaza’s coast, he said. An Israeli helicopter touched down near the U.S.-built pier and helped whisk away hostages and the commando, according to the U.S. and Israeli militaries.

For the U.N. and independent humanitarian groups, the event made real one of their main doubts about the U.S. sea route: whether aid workers could cooperate with the U.S. military-backed, Israeli military-secured project without violating core humanitarian principles of neutrality and independence and without risking aid workers becoming seen as U.S. and Israeli allies — and, in turn, targets in their own right.

Israel and the U.S. deny that any aspect of the month-old U.S. pier was used in the Israeli raid. They say an area near it was used to fly home the hostages.

The U.N. World Food Program, which works with the U.S. to transfer aid from the $230 million pier to warehouses and local aid teams for distribution within Gaza, suspended cooperation as it conducts a security review. Aid has been piling up on the beach since.

“You can be sure we are going to be very careful about what we assess and what we conclude,” U.N. humanitarian chief Martin Griffiths said.

Griffiths told reporters at an aid conference in Jordan this week that determining that the Israeli raid improperly used either the beach or roads around the pier “would put at risk any future humanitarian engagement in that operation.”

The U.N. has to look at the facts as well as what the Palestinian public and militants believe about any U.S., pier or aid worker involvement in the raid, spokesman Farhan Haq told reporters in New York.

“Humanitarian aid must not be used and must not be perceived as taking any side in a conflict,” Haq said. “The safety of our humanitarian workers depends on all sides and the communities on the ground trusting their impartiality.”

Rumors have swirled on social media, deepening the danger to aid workers, humanitarian groups say.

“Whether or not we’ve seen the pier used for military purposes is almost irrelevant. Because the perception of people in Gaza, civilians and armed groups, is that humanitarian aid has been instrumentalized” by parties in the conflict, said Suze van Meegen, head of operations in Gaza for the Norwegian Refugee Council.