The United States warned Israel on Tuesday that it could withhold some of its billions of dollars in military assistance unless it improves aid delivery to the Gaza Strip within 30 days.
The warning comes a year into Israel's war on Gaza, in which President Joe Biden has repeatedly pleaded with Israel to spare Palestinian civilians.
In a letter sent Sunday, Secretary of State Antony Blinken and Defence Secretary Lloyd Austin made "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," State Department spokesman Matthew Miller told reporters.
The letter pointed to US law requiring that "recipients of US military assistance do not arbitrarily deny or impede provisioning of US humanitarian assistance."
"Our hope is that Israel will make changes that we have outlined and that we have recommended, and as a result of those changes will be a dramatic increase in humanitarian assistance."
The letter addressed to Israeli Defence Minister Yoav Gallant was first reported by Axios, with the State Department saying it was intended to remain private.
In the letter, Blinken and Austin urge Israel to let at least 350 trucks of aid enter per day, to open a fifth crossing into Gaza and to rescind evacuation orders to Palestinians when there is no operational need.
The State Department said that earlier US pressure allowed the entry of 300 to 400 trucks per day but that overall aid has fallen by more than 50 percent from its peak.
Repeated US warnings
Biden has been among the strongest international backers of Israel since the start of the war on Gaza.
The letter asks for action within 30 days, meaning any evaluation would come after the US election in which Biden's Democratic Party has faced accusations that it has not done enough to rein in Israel.
Vice President Kamala Harris, in a tight race to succeed Biden, also voiced alarm over the weekend at a UN assessment that no food has entered northern Gaza in nearly two weeks.
"Israel must urgently do more to facilitate the flow of aid to those in need," Harris wrote on X, formerly Twitter.
Miller denied any election link on the timing, saying: "We didn't think it was appropriate to send a letter and just say this has to happen overnight."
Suggesting that US pressure bears fruit, Miller pointed to Israel allowing assistance through the Erez crossing into Gaza on Monday, one day after Blinken and Austin sent the letter.
However, some say that the United States has far more leverage that it can exert and that Israeli Prime Minister Benjamin Netanyahu has repeatedly brushed aside pressure.
After months of warning Israel against a wider conflict with Iran, Biden over the weekend authorised deployment of the THAAD missile defence system to Israel, marking the first dispatch of US troops, however temporarily, in the conflict.
The State Department also said on Tuesday it had voiced concerns with Israel over airstrikes in the Lebanese capital Beirut, although it has stopped short of calling for a ceasefire and backed Israel's right to hit Hezbollah.
"We have made clear that we are opposed to the campaign the way we've seen it conducted over the past weeks" in Beirut, Miller said.
He also said that Blinken had viewed footage, widely shared on social media, that showed at least one Palestinian burned alive after an Israeli strike set ablaze tents outside a hospital in central Gaza.
"We all saw that video, and all know that it's horrifying to see people burned to death. We have made clear our serious concerns about the matter directly with the government of Israel."