The United States on Sunday pressed Israel to protect civilians in Gaza and pushed for an immediate increase in humanitarian aid, amid a growing outcry over the human costs of Israel's three-week bombardment of the enclave.

President Joe Biden told Israeli Prime Minster Netanyahu in a call that Israel has a right to defend itself and should do so in a way that is consistent with international law on protecting civilians, the White House said.

Biden and Netanyahu discussed efforts to protect the more than 200 hostages seized by Palestinian Hamas militants in a surprise attack on Israel on Oct. 7 that killed 1,400 people.

The White House said Biden also "underscored the need to immediately and significantly increase the flow of humanitarian assistance to meet the needs of civilians in Gaza," as supplies dwindle in the besieged coastal enclave.

With the death toll in the Gaza Strip in the thousands and climbing, Biden's administration has been under increasing pressure to make clear that its steadfast support of Israel does not translate into a blanket endorsement of all that its ally is doing in the impoverished enclave.

In television interviews earlier on Sunday, Biden's national security adviser, Jake Sullivan, said Israel has a responsibility to protect the lives of innocent people in Gaza.

Washington was asking hard questions of Israel, including on issues surrounding humanitarian aid, distinguishing between terrorists and innocent civilians and on how Israel is thinking through its military operation, Sullivan said.

"What we believe is that every hour, every day of this military operation, the IDF (Israel Defense Forces), the Israeli government should be taking every possible means available to them to distinguish between Hamas terrorists who are legitimate military targets and civilians who are not," he said on CNN.

Sullivan also said Netanyahu has a responsibility to "rein in" extremist Jewish settlers in the Israeli-occupied West Bank. "It is totally unacceptable to have extremist settler violence against innocent people in the West Bank," he said.

Biden is facing pressure from within his own Democratic Party to call for a ceasefire.

As Israel's largest military backer, the United States bears some responsibility for its actions in Gaza, U.S. Representative Pramila Jayapal, leader of the Congressional Progressive Caucus, said on NBC's "Meet the Press."

"We are losing credibility," Jayapal said. "And, frankly, we're being isolated in the rest of the world."

The attack from Gaza's Hamas rulers unleashed a wave of aerial bombardment from Israel and an incipient ground operation.

Medical authorities in the Gaza Strip, which has a population of 2.3 million people, say 8,005 Palestinians have been killed in Israel's campaign to obliterate Iran-backed Hamas.

Hamas militants have embedded themselves among the Palestinian population and in civilian infrastructure, making an operation against them extremely difficult, Sullivan said.

"That creates an added burden for Israel, but it does not lessen Israel's responsibility under international humanitarian law, to distinguish between terrorists and civilians, and to protect the lives of innocent people, and that is the overwhelming majority of the people in Gaza," Sullivan said.

With supplies of food, water and medicines running low, thousands of Gaza residents broke into UN warehouses and distribution centers to get food.

There has been a mounting international outcry over the toll from the bombing and growing calls for a "humanitarian pause" to allow aid to reach Gaza civilians.

In an interview on CBS, Sullivan was asked if there was "daylight" between the United States and the Netanyahu government, Sullivan responded, ""We talk candidly, we talked directly, we share our views in an unvarnished way and we will continue to do that."

"But sitting here in public, I will just say that the United States is going to make its principles and propositions absolutely clear, including the sanctity of innocent human life. And then we will continue to provide our advice to Israel in private."