The Biden administration’s policy on Gaza has been widely criticised as being in disarray as the defense secretary described the situation as a “humanitarian catastrophe” the day after the state department declared Israel to be in compliance with international humanitarian law.

Washington was also on the defensive on Tuesday over its claim that a UN security council ceasefire resolution on which it abstained was non-binding, an interpretation that put the US at odds with other member states, international legal scholars and the UN itself.

Analysts said the strain was increasingly showing as the administration sought to maintain a policy that aims to influence Israel’s actions and prevent a full-scale famine in Gaza, while avoiding the use of leverage, like the restriction of arms supplies, which could have political repercussions at home in an election year.

Jeremy Konyndyk, a former senior Biden official now president of the Refugees International aid advocacy group, said “the strategy is a mess”.

“The US is talking a big game about fighting the famine that its bombs and diplomatic cover have helped create,” Konyndyk said on the X social media platform. “This is not how you fight a famine. This is dithering while people starve.”

Lloyd Austin, the US defense secretary, acknowledged the depth and urgency of the crisis on Tuesday when he met his Israeli counterpart, Yoav Gallant, at the Pentagon.

“Gaza is suffering a humanitarian catastrophe and the situation is getting even worse,” Austin told Gallant in remarks in front of the press, calling for a significant expansion in aid deliveries by land.

Under US pressure, Israel has opened a third land crossing into Gaza, Gate 96, giving access to the north, but continues to limit the scale of aid convoys going through it – through restrictions on items it deems to be of dual use, nominating a small number of drivers allowed to use the crossing and other procedural requirements.

I​​srael announced on Monday it would stop working with the UN relief agency Unrwa, the main aid agency serving Gaza. Unrwa said its aid convoys had been blocked since 21 March.

On the same day, the state department spokesman, Matthew Miller, insisted that the US currently had no reason to dispute Israeli assurances that it was complying with humanitarian law in Gaza.

“We have not found them to be in violation of international humanitarian law, either when it comes to the conduct of the war or when it comes to the provision of humanitarian assistance,” Miller said.

The US assessment is critical under a national security memorandum issued by Joe Biden in February, known as NSM-20, requiring “credible and reliable written assurances” from countries receiving US weapons that they would use “any such defense articles in accordance with international humanitarian law”.

One of the criteria was that the “recipient country will facilitate and not arbitrarily deny, restrict, or otherwise impede, directly or indirectly, the transport or delivery of US humanitarian assistance and US government-supported international efforts to provide humanitarian assistance”.

If the secretaries of state or defense deem the relevant country’s compliance had been “called into question”, arms supplies could be suspended.

Miller’s remarks on Israeli assurances drew outrage from aid organisations and some progressive members of Congress.

“To pretend that Israel is not violating international law or interfering with US humanitarian aid is absurd on its face,” Senator Bernie Sanders said. “The state department’s position makes a mockery of US law and assurances provided to Congress.”

Miller said there were “ongoing processes” for assessing the legality of Israeli military operations in Gaza, a reference to a review mechanism set up by the administration in September, called Civilian Harm Incident Response Guidance.

“As of yet, we have not made a conclusion that Israel is in violation of international humanitarian law,” Miller said, but added that the review process would continue and that a full report on compliance required by the presidential memorandum was not due until 8 May.

Chris Van Hollen, a Democratic senator, said there was ambiguity about the state department’s position but if it was saying Israel was currently in compliance under the terms of NSM-20, “their decision is totally detached from the reality on the ground, especially with respect to the required standards for the delivery of humanitarian aid into and within Gaza”.

Dylan Williams, vice-president for government affairs at the Center for International Policy, said: “Treating the assurances received from Israel as sufficient in the face of deepening famine, disproportionate civilian casualties and repeated threats of an offensive in Rafah against US wishes renders NSM-20 an empty gesture in its first outing, and functionally greenlights Israel continuing to use our weapons against US law, interests and values.”