US President Joe Biden pressed on with plans for a troubled aid pier for Gaza despite internal warnings, a watchdog said, as the White House defended the operation Wednesday as a "comprehensive response" to a humanitarian crisis.

Biden expressed disappointment with the performance of the pier operated by the US military, which repeatedly had to be removed from shore due to bad weather.

But the watchdog for the US Agency for International Development (USAID) said in the report released Tuesday that there had been a series of warnings about rough seas and security challenges before Biden decided to deploy the problematic pontoon.

"Multiple USAID staff expressed concerns" about the fact that the pier would distract from pushing Israel to open land crossings, a "more efficient and proven" way of getting aid to desperate Gaza, it said.

"Once the president issued the directive, the Agency's focus was to use (the pier) as effectively as possible."

The White House said Wednesday the pier was "part of a comprehensive response to dire conditions alongside air and land deliveries."

The pier delivered nearly 20 million pounds (nine million kilograms) of food and water and "significantly helped alleviate" conditions in northern Gaza at a time when experts were warning of imminent famine, National Security Council spokesman Sean Savett said.

"We are grateful to the heroic efforts of the men and women of the US military who built and maintained the pier," he added.

Biden announced the project during his State of the Union address in March as Israel held up deliveries of assistance by land.

But the USAID report said the pier problems meant it "fell short" of its goal of giving half a million Palestinians enough aid for three months, supplying only enough to feed 450,000 for one month.

In the end the pier was only operational for 20 days during the two months before it was decommissioned, said the report.

"From the start, rough weather posed a major challenge," it said, adding that the pier was "detached or was shut down numerous times."

Pentagon guidance discussed at an initial planning meeting had said the pier was only suitable for use in short or moderate waves -- but the Mediterranean often has "significant" winds and waves, the watchdog said.

Security concerns in an active war zone where Israel was striking Hamas after the October 7 attacks "significantly impacted" aid delivery through the pier, it added.