Senior United States officials have warned Israel that if it does not take “urgent and sustained actions” to allow more humanitarian assistance into the Gaza Strip, the US government may be forced to curtail its support for the top ally.

The warning, put forward in a letter signed by Secretary of State Antony Blinken and Pentagon chief Lloyd Austin that was made public this week, came as Israel’s year-long war on Gaza has fuelled starvation and disease across the coastal Palestinian enclave.

“The amount of assistance entering Gaza in September was the lowest of any month during the past year,” the US officials said in the letter, giving Israel 30 days to act on a series of demands to “reverse the downward humanitarian trajectory”.

Almost immediately, lawyers, human rights advocates and other experts questioned the US administration’s apparent threat of cutting off American military assistance to Israel.

“Once again, the Biden administration is doing bureaucratic gymnastics to avoid enforcing US law and ending arms transfers to Israel,” Annie Shiel, US advocacy director at the Center for Civilians in Conflict, said in a social media post.

“Meanwhile, thousands more Palestinian civilians will be killed, maimed, and starved during these 30 days.”

While the US is required under its own laws to suspend military assistance to a country if that country restricts the delivery of American-backed humanitarian aid, US President Joe Biden’s administration has so far refused to apply that rule to Israel, experts note.

So what is this week’s letter all about, how have stakeholders and experts responded, and what could come next? Here’s what you need to know.

What did the letter say?

Blinken and Austin acknowledged the dire humanitarian crisis in Gaza, including the risks faced by 1.7 million people who have been forced, through multiple evacuation orders, into a narrow coastal area in the bombarded territory.

They said they were “particularly concerned” that recent Israeli actions “are contributing to an accelerated deterioration” in conditions. Those actions include Israel blocking commercial imports into Gaza, and “denying or impeding nearly 90 percent of humanitarian movements between northern and southern Gaza in September”.

The letter called on the Israeli government to institute a series of measures over the next 30 days, including:

• Allowing a minimum of 350 trucks to enter Gaza per day
• Providing for “adequate humanitarian pauses” that will allow humanitarian deliveries and distribution to take place, for at least the next four months
• Rescinding evacuation orders “when there is no operational need”

The US leaders also asked Israel to “end [the] isolation of northern Gaza” – where Israeli forces recently launched an intensified assault – by allowing humanitarian groups to access the area and affirming there is no Israeli government plan to force Palestinian civilians out.

What US law is Israel accused of violating?

In their letter, Blinken and Austin cited Section 620I of the US Foreign Assistance Act, a law that oversees the country’s provision of foreign aid.

“No assistance shall be furnished under this Act or the Arms Export Control Act to any country when it is made known to the President that the government of such country prohibits or otherwise restricts, directly or indirectly, the transport or delivery of United States humanitarian assistance,” the section reads.

The act offers an exception to the rule, allowing assistance to continue to flow to a country if a US president determines that doing so is in the United States’s national security interest. But the president must notify congressional committees that such a decision was made and why.

Biden has not invoked that waiver in the case of Israel’s war on Gaza.

The US provides Israel with at least $3.8bn in military assistance annually, and Biden has approved an additional $14bn in aid since the war in Gaza began in early October 2023.

What is happening on the ground in Gaza?

Israel has denied blocking humanitarian aid deliveries to Gaza, with its COGAT agency that oversees deliveries saying it will continue expanding “efforts to facilitate humanitarian aid across Gaza”.

However, the United Nations and other humanitarian aid groups for months have accused the country of impeding their efforts to get food, water, medicine and other critical assistance to Palestinians.

Concerns over a worsening humanitarian crisis recently escalated after the Israeli military issued more evacuation orders and tightened its siege on northern Gaza as it launched a renewed ground offensive in the area.

On Thursday, the UN’s hunger monitoring system, known as the Integrated Food Security Phase Classification (IPC), said 1.84 million Palestinians in Gaza faced high levels of acute food insecurity. Of that, 133,000 were experiencing “catastrophic” insecurity.

Heba Morayef, the Middle East and North Africa director at Amnesty International, warned that Israel was “forcing civilians to choose between starvation or displacement, while their homes and streets are relentlessly pounded by bombs and shells”.

Joyce Msuya, the UN’s acting humanitarian chief, told the Security Council this week that across Gaza, “less than a third of the 286 humanitarian missions coordinated with Israeli authorities in the first two weeks of October were facilitated without major incidents or delays”.

“Every time a mission is impeded, the lives of people in need and humanitarians on the ground are put at even greater risk,” Msuya said.

Last month, 15 aid groups – including Save the Children, Oxfam and the Norwegian Refugee Council – also reported that “Israel’s systematic aid obstruction” has meant that 83 percent of required food aid does not make it into Gaza.

“A record low average of 69 aid trucks per day entered Gaza in August 2024, compared to 500 per working day last year; which was already not enough to meet people’s needs. In August more than 1 million people did not receive any food rations in southern and central Gaza,” they said.

What have experts said about this week’s US letter?

Annelle Sheline, a former US State Department official who resigned over the administration’s Gaza policy, said this week’s letter is a “clear acknowledgement that the administration knows 620i is being violated”.

“Under US law, this renders Israel ineligible to receive American weapons or security assistance,” she wrote on social media.

Others questioned why Washington has given Israel 30 days to allow more humanitarian assistance into Gaza before it cuts off military assistance, despite evidence showing deliveries are being hampered.

“If [Biden] was serious he would’ve already done it, as required by law,” said Matt Duss, executive vice president of the Center for International Policy, a think tank in Washington, DC.

“After 30 days they’ll thank Israel for easing some restrictions (which still won’t meet the legal requirement) and keep the ammunition flowing,” he added on the social media platform X.

Sarah Leah Whitson, a lawyer and executive director of the US-based think tank DAWN, also said that while the letter marked “an important and unprecedented signal that Israel has crossed even the Biden administration’s permissive red lines”, concrete action is still needed.

“We now need the Biden administration to show action, not just words, in enforcing US laws, which prohibit aid to Israel given not only its relentless obstruction of humanitarian relief but deliberate starvation and incessant bombardment of Gaza’s civilians,” she said in a statement.

Why was the letter issued now?

The dire conditions in northern Gaza – and fears that Israel’s siege on the area would put hundreds of thousands of Palestinians at risk – have put a renewed spotlight on humanitarian aid restrictions.

Speaking at the UN Security Council this week, US ambassador Linda Thomas-Greenfield said “a ‘policy of starvation’ in northern Gaza would be horrific and unacceptable and would have implications under international law and US law”.

“The Government of Israel has said that this is not their policy, that food and other essential supplies will not be cut off, and we will be watching to see that Israel’s actions on the ground match this statement,” she said.

Critics have accused Israel of enforcing a plan, devised by former generals, that calls for starving people in northern Gaza in order to force residents to evacuate the area and declare it as a closed military zone.

The Associated Press news agency reported earlier this week that Israeli Prime Minister Netanyahu was “examining” the scheme, dubbed the “General’s Plan”.

The Biden administration’s letter also comes just a few weeks before the US presidential election, which will see Democratic Vice President Kamala Harris go up against Republican former President Donald Trump.

The Biden administration’s staunch backing of Israel has been a major source of criticism ahead of next month’s vote, with Harris facing calls to increase pressure on Israel to end the war, including by suspending weapons transfers to the US ally.

But Harris has rejected that demand and continued to express strong support for Israel despite warnings that her stance could cost her much-needed votes from progressives as well as Arab and Muslim Americans.