In a rare, direct threat, the Biden administration has told Israel it must allow humanitarian aid into the besieged Gaza Strip or risk losing U.S. military armament, U.S. officials said Tuesday.

The demand comes as Israel launches another major offensive in northern Gaza, where airstrikes in recent days have hit a school, refugee camp and a food repository. Aid agencies say tens of thousands of civilians face hunger and starvation.

U.S. officials say badly needed food, medicine and other aid has been all but cut off for weeks. Although officials have repeatedly pressed Israel to allow more deliveries, only scant amounts have trickled in. Israeli officials have argued that any aid benefits Hamas.

The Biden administration is telling Israel it has 30 days to step up deliveries of aid, aiming for 350 truckloads a day. Only about 40 truckloads entered the coastal enclave on a single recent day.

Trucks carrying humanitarian aid to the Gaza Strip pass through the inspection area at the Kerem Shalom crossing in southern Israel in March.

(Ohad Zwigenberg / Associated Press)

The ultimatum is contained in a letter from Secretary of State Antony J. Blinken and Defense Secretary Lloyd J. Austin III sent to their Israeli counterparts over the weekend.

They called for “urgent and sustained actions” to reverse months of decline in aid shipments and general deterioration of conditions.

U.S. law prohibits military aid to countries that block the delivery of U.S. humanitarian assistance to a zone in need.

The warnings come amid Israeli media reports that Prime Minister Benjamin Netanyahu is considering a plan to order the complete evacuation of northern Gaza, followed by cutting off all food and water to the region in an attempt to root out all remaining Hamas militants. Civilians who did not flee would be considered militants. It was unclear if the government was seriously considering the plan.

Efforts in April by Biden administration officials to force Israel to step up aid were only marginally successful.

“What we have seen over the past few months is that the level of humanitarian assistance has not been sustained,” U.S. State Department spokesman Matthew Miller said Tuesday. “In fact, it has fallen by over 50% from where it was at its peak.”

There are numerous impediments to aid distribution, including raging combat and Israeli airstrikes. Israel only slowly and sparingly opens crossings into Gaza, an area sealed off from outside access. Hamas sometimes hijacks shipments or demands payments of protection money, and supplies are often looted. Agencies working in the field are also worried about their own safety.

Palestinians line up for food during the ongoing Israeli air and ground offensive on the Gaza Strip in Rafah in January.

(Hatem Ali / Associated Press)

“But the answer to [security concerns] is not to stop the flow of food and water that civilians depend on and that little babies and children need to survive,” Miller said. “That cannot be the answer to that problem.”

Ever since Hamas attacked southern Israel a year ago and set off the war in Gaza, President Biden has repeatedly urged Israel to limit civilian casualties, to agree to a cease-fire, to limit invasions of parts of Gaza and increasingly to facilitate aid deliveries. Most of Biden’s entreaties have been largely ignored by Israel’s right-wing government.

Earlier this year, when Biden briefly suspended the shipment of 2,000-pound bombs to Israel to avoid their use in crowded Gaza towns, he was met with a firestorm of protest from conservative Republicans. At the same time, many American progressives and others have been demanding the U.S. suspend arm shipments to Israel altogether because of the death toll among Palestinian civilians in Gaza. An estimated 42,000 have been killed, according to Gaza’s Health Ministry, which does not distinguish between civilians and combatants but says over half of the dead are women and children.

Israel receives around $3 billion annually in mostly military aid from the United States.