President Joe Biden's administration last month issued a directive for countries that receive US military aid to make "credible and reliable" assurances that they are complying with human rights laws, following concerns over the toll on civilians in Israel's Gaza campaign.

The State Department confirmed that Israel and six other countries that receive US military aid -- Colombia, Iraq, Kenya, Nigeria, Somalia and Ukraine -- had submitted written assurances by a Sunday deadline.

"In each case, these assurances were made by a credible high-level official in the partner government who has the ability and authority to make decisions and commitments about the issues at the heart of the assurances," State Department spokesman Matthew Miller told reporters.

He said that the administration, in accordance with the directive, known as National Security Memorandum-20, or NSM-20, would provide a report to Congress by May 8.

Miller offered no indication the Biden administration was rejecting Israeli assurances.

"We have not found them to be in violation of international humanitarian law, either when it comes to the conduct of the war or when it comes to the provision of humanitarian assistance," Miller said.

The United States is the top military and diplomatic support of Israel, although Prime Minister Benjamin Netanyahu voiced anger Monday that Washington did not veto a UN Security Council resolution that demanded a ceasefire for the ongoing month of Ramadan.

Israel has been waging a relentless military campaign in Gaza in response to Hamas's surprise attack on October 7 that was the deadliest in Israeli history.

Seventeen senators ahead of the deadline had pressed the Biden administration not to immediately describe Israel's assurances as credible, saying that US security assistance "should be used to advance our interests and values."

UN predictions of an imminent famine in Gaza "make it abundantly clear that Netanyahu's government is not doing nearly enough to allow aid to reach starving and otherwise desperate people in Gaza," said a letter led by Democratic Senator Chris Van Hollen whose signatories included Tim Kaine, Dick Durbin and Bernie Sanders.

"As a result, we believe it would be inconsistent with the letter and spirit of NSM-20 to find that assurances made by the Netanyahu government meet the required 'credible and reliable' standard at this time," they wrote.