The United States has told Israel it must take steps in the next month to improve the humanitarian situation in Gaza or face potential restrictions on U.S. military aid, U.S. officials said, in the strongest such warning since Israel's war with Hamas began a year ago.

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

The top UN humanitarian official is accusing Israel of blocking the delivery of desperately needed aid to Gaza, and the US ambassador is demanding that its government step up efforts to tackle the Palestinian territory’s ”intolerable and catastrophic humanitarian crisis.

The first aid in two weeks was allowed into northern Gaza following the letter, but the UN's acting humanitarian chief Joyce Msuya described it as a “trickle”. In the letter sent on Sunday, the US expressed deep concern at the humanitarian situation and said Israeli actions had contributed to it.

The Biden administration warned Israel this week that Washington could suspend military assistance if humanitarian aid flows in Gaza are not increased within a month.

There was no official response from the Israeli government, a day after the United States threatened consequences if it didn’t let more relief into Gaza within 30 days.