WASHINGTON (AP) — The Biden administration has warned Israel that it must increase the amount of humanitarian aid it is allowing into Gaza within the next 30 days or it could risk losing access to U.S. weapons funding.

Secretary of State Antony Blinken and Defense Secretary Lloyd Austin warned their Israeli counterparts in a letter dated Sunday that the changes must occur. The letter, which restates U.S. policy toward humanitarian aid and arms transfers, was sent amid deteriorating conditions in northern Gaza and reports Israel had conducted a strike on a hospital tent site in central Gaza that killed at least four people and ignited a fire that left more than two dozen with severe burns.

A senior defense official said Tuesday that Blinken and Austin sent a letter to their Israeli counterparts as they saw a recent decrease in assistance reaching Gaza. The official said a similar letter sent by Blinken in April triggered a constructive response and "concrete measures from the Israelis."

The official, who spoke on condition of anonymity to discuss internal deliberations, said the latest letter was a way to similarly address the problem.

For Israel to continue qualifying for foreign military financing, the level of aid getting into Gaza must increase to at least 350 trucks a day, Israel must institute additional humanitarian pauses and provide increased security for humanitarian sites, Austin and Blinken said. They said Israel had 30 days to respond to the requirements.

An Israeli official confirmed a letter had been delivered but did not discuss the contents. That official, speaking on condition of anonymity to discuss a diplomatic matter, confirmed the U.S. had raised "humanitarian concerns" and was putting pressure on Israel to speed up the flow of aid into Gaza.

The letter, which an Axios reporter posted a copy of online, was sent during a period of growing frustration in the administration that despite repeated and increasingly vocal requests to scale back offensive operations, Israel’s bombardment has led to unnecessary civilian deaths and risks plunging the region into a much wider war.

“We are particularly concerned that recent actions by the Israeli government, including halting commercial imports, denying or impeding 90 percent of humanitarian movements” and other restrictions have kept aid from flowing, Blinken and Austin said.

The Biden administration is increasing its calls for its ally and biggest recipient of U.S. military aid to ease the humanitarian crisis in Gaza while assuring that America's support for Israel is unwavering just before the U.S. presidential election in three weeks.

Funding for Israel has long carried weight in U.S. politics, and Biden said this month that "no administration has helped Israel more than I have."

Humanitarian aid groups fear that Israeli leaders may approve a plan to seal off humanitarian aid to northern Gaza in an attempt to starve out Hamas, which could trap hundreds of thousands of Palestinians who are unwilling or unable to leave their homes without food, water, medicine and fuel.

U.N. humanitarian officials said last week that aid entering Gaza is at its lowest level in months. About 80 trucks carrying aid have entered through crossings in Gaza’s north since Oct. 1, down from roughly 60 trucks a day previously, according to the U.N. website tracking deliveries.

COGAT, the Israeli body facilitating aid crossings into Gaza, denied that crossings to the north have been closed.

U.S. officials said the letter was sent to remind Israel of both its obligations under international humanitarian law and of the Biden administration’s legal obligation to ensure that the delivery of American humanitarian assistance should not be hindered, diverted or held up by a recipient of U.S. military aid.

Israel’s retaliatory offensive since the Oct. 7, 2023, attacks by Hamas has killed nearly 42,000 people in Gaza, according to the territory’s Health Ministry, which does not distinguish between civilians and combatants in its count. The Hamas attacks that launched the war killed some 1,200 people, mostly civilians, and militants abducted another 250.

The United States has spent a record total of at least $17.9 billion on military aid to Israel since the war in Gaza began and led to escalating conflict around the Middle East, according to a report for Brown University's Costs of War project.

That aid has enabled Israel to purchase billions of dollars worth of munitions it has used in its operations against Hamas in Gaza and Hezbollah in Lebanon. However many of those strikes also have killed civilians in both areas.

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AP reporter Josef Federman in Jerusalem contributed.