WASHINGTON (Reuters) - A part of the U.S. military's pier off Gaza has broken off, rendering it temporarily inoperable, two U.S. officials said, in the latest blow to efforts to deliver humanitarian aid to Palestinians.

The U.S. officials, who spoke on condition of anonymity, said bad weather was believed to be the reason that the part had broken off. They did not say how big the part was or speculate on how long it would take for the pier to resume operations.

The pier was announced by U.S. President Joe Biden in March and involved the military assembling the floating structure off the coast. Estimated to cost $320 million for the first 90 days and involve about 1,000 U.S. service members, it went into operation two weeks ago.

Since the pier began operations, the United Nations has transported 137 trucks of aid from the pier - the equivalent of 900 metric tonnes - said a U.N. World Food Programme (WFP) spokesperson.

(Reporting by Idrees Ali and Phil Stewart; Editing by David Holmes)