The US has written to Israel giving it 30 days to improve access to humanitarian aid in Gaza or risk having some US military aid cut off.

The letter sent Sunday represents the strongest known written warning from the United States to its ally and comes amid a new Israeli offensive in the northern Gaza Strip that has reportedly caused large numbers of civilian casualties.

It said the US was deeply concerned about the deteriorating humanitarian situation, adding that Israel had denied or obstructed nearly 90% of humanitarian movements between the north and south over the past month.

Israel is reviewing the letter, an Israeli official said, adding that the country “takes this matter seriously” and intends to address “the concerns raised” with its U.S. counterparts.

Israel has previously said it is targeting Hamas militants in the north and is not stopping the flow of humanitarian aid.

On Monday, the Israeli military agency Cogat, which is responsible for managing the border crossings into Gaza, said that 30 trucks carrying aid from the World Food Program had entered the north of the Gaza Strip through the Erez border crossing.

That ended a two-week period in which, according to the UN, food aid was not delivered to the north and essential supplies for the 400,000 Palestinians there were running low.

The U.S. is by far the largest arms supplier to Israel, and the Israeli military relied heavily on U.S.-supplied planes, guided bombs, rockets and grenades in last year's war against Hamas in Gaza.

The US letter to the Israeli government – the contents of which have now been confirmed by the State Department – was first reported on the Axios website. It is signed by Secretary of State Antony Blinken and Secretary of Defense Lloyd Austin.

“We write now to underscore the U.S. government’s deep concerns about the deteriorating humanitarian situation in Gaza and call for urgent and sustained action by your government this month to reverse this trend,” it said.

It says that Israeli evacuation orders have forced 1.7 million people into the narrow coastal area of ​​al-Mawasi, where extreme overcrowding puts them at “high risk of fatal infection,” and that humanitarian organizations report that their survival needs are not being met can be covered.

“We are particularly concerned about the Israeli government’s recent actions – including halting commercial imports, denying or obstructing nearly 90% of humanitarian movements between the northern and southern Gaza Strip in September, maintaining burdensome and excessive dual-use restrictions, as well “The introduction of new and burdensome checks.” Liability and customs regulations on humanitarian personnel and supplies – along with increasing lawlessness and looting – are contributing to an accelerated deterioration of conditions in Gaza,” it said.

The letter says that Israel must take a series of concrete actions “starting immediately and within 30 days” to increase aid deliveries, adding that failure “could have implications for U.S. policy.”

It cites U.S. laws that can prohibit military aid to countries that impede the delivery of U.S. humanitarian aid.

It says that Israel must “increase all forms of humanitarian assistance across the Gaza Strip” before winter, including by allowing at least 350 trucks per day to enter through all four major border crossings and a new fifth border crossing, and to help people in all areas. Mawasi allows entry to move inland.

It also calls on Israel to end the “isolation of the northern Gaza Strip” by reaffirming that there will be “no Israeli government policy of forced evacuation of civilians” from north to south.

At a news conference in Washington on Tuesday, State Department spokesman Matthew Miller told reporters that the letter was “a private diplomatic communication that we did not intend to make public.”

“Secretary (Blinken), along with Secretary Austin, saw fit to make it clear to the Israeli government that it must again make changes to increase the level of aid entering Gaza,” he said.

Mr. Miller declined to speculate on what consequences Israel might face if access to humanitarian aid is not improved.

But he noted: “Recipients of U.S. military assistance do not arbitrarily deny or impede the provision of U.S. humanitarian assistance.” That is simply the law and we will of course abide by the law. But we hope that Israel will implement the changes we have outlined.”

He also said the 30-day deadline was not linked to the upcoming US presidential election on November 5, saying it was “appropriate to give them time to deal with the various issues”.

Israel has previously insisted that there are no limits on the amount of aid or humanitarian assistance that can be delivered to and within the Gaza Strip, blaming UN agencies for failing to distribute aid. It also accuses Hamas of stealing aid funds, which the group denies.

Ahead of Israel's ground offensive in the southern Gaza town of Rafah in May, President Joe Biden deployed a single shipment of 2,000- and 500-pound bombs for the first time in an attempt to dissuade the country from a major attack.

But the president immediately faced a backlash from Republicans in Washington and Israeli Prime Minister Benjamin Netanyahu, who appeared to compare it to an “arms embargo.” The suspension was partially lifted in July and was not repeated.

Earlier on Tuesday, the International Committee of the Red Cross (ICRC) warned that families in the northern Gaza Strip were facing “unimaginable fear, loss of loved ones, confusion and exhaustion” due to the Israeli offensive that began 10 days ago.

The Israeli military says it has sent tanks and troops into the town of Jabalia and its urban refugee camp for the third time to root out Hamas militants who have regrouped there.

It has ordered residents of Jabalia and neighboring Beit Lahia and Beit Hanoun to evacuate to the “humanitarian area” of al-Mawasi.

About 50,000 people have fled to Gaza City and other parts of the north, according to the United Nations. But for many, it is unsafe to leave their home or they are unable to leave because they are ill or disabled.

Khalid, a Jabalia resident whose accounts of the past year are featured in a new BBC documentaryHe said in a voice note that he and his family had been living in fear for a week.

“We were told to go south, but we couldn't because the Israeli army surrounded the area, either with earth barricades or with quadcopter drones. We can’t move, it’s too difficult.”

“At the same time, we live in constant fear due to the intense bombing. My daughter has become ill and has a fever. Her whole body is shaking in fear because of the noise of the bombings and I don't know what to do with her. I can’t even take her to the hospital,” he added.

The Hamas-run Civil Defense Authority in the Gaza Strip said its first responders on Tuesday recovered the bodies of 42 people killed by Israeli air and artillery strikes in Jabalia and neighboring areas.

These were reportedly 11 members of the same family, almost all women and children, whose home was destroyed in an airstrike overnight.

The Israeli military said on Tuesday that its troops had killed “dozens of terrorists” in the Jabalia area the previous day.

On Monday, Israeli human rights groups warned of “alarming signs that the Israeli military is beginning to quietly implement the generals' plan.”reflecting widespread Palestinian concerns.

The controversial plan calls for the forcible relocation of all civilians in the north, followed by a siege of Hamas fighters who remain there to force their surrender and the release of Israeli hostages.

The Israeli military denies the implementation, saying it only aims to “get civilians out of harm’s way.”

In response to Hamas's unprecedented attack on southern Israel on October 7, 2023, in which approximately 1,200 people were killed and 251 others were taken hostage, Israel launched a campaign to destroy Hamas.

More than 42,340 people have been killed in Gaza since then, according to the territory's Hamas-run health ministry.