WASHINGTON >> 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 an Israeli airstrike on a hospital tent site in central Gaza that killed at least four people and burned others.

A similar letter that Blinken sent to Israeli officials in April led to more humanitarian assistance getting to the Palestinian territory, State Department spokesman Matthew Miller said Tuesday. But that has not lasted.

“In fact, it’s fallen by over 50% from where it was at its peak,” Miller said at a briefing. “So the secretary, along with Secretary Austin, thought it was appropriate to make clear to the government of Israel that there are changes that they need to make again, to see that the level of assistance making it into Gaza comes back up from the very, very low levels that it is at today.”

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 in their letter. They said Israel had 30 days to respond to the requirements.

“The letter was not meant as a threat,” White House national security spokesman John Kirby told reporters. “The letter was simply meant to reiterate the sense of urgency we feel and the seriousness with which we feel it, about the need for an increase, a dramatic increase in humanitarian assistance.”

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 against Hamas, 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.