In his final months in office, President Joe Biden is signalling a new willingness to use U.S. military assistance to Israel as both a carrot and a stick to influence its high-stakes confrontation with Iran and Iran-backed militant groups.

But while the approach increases Washington's involvement in Israeli decision-making just weeks before the US presidential election, it is unclear whether it will help achieve Biden's goals, including preventing a broader regional conflict and getting Israel to address the increasingly dire humanitarian situation in Gaza, experts say.

Biden's administration announced on Sunday it would send about 100 soldiers to Israel along with an advanced U.S. anti-missile system, a rare deployment that came as Prime Minister Benjamin Netanyahu's government weighs a retaliatory attack on Iran after an Oct. 1 Iranian missile strike.

The Biden administration also delivered Israel a letter on Sunday warning that it must take steps in the next month to improve the humanitarian situation in Gaza or face potential restrictions on U.S. military aid.

Publicly, U.S. officials say the seemingly opposing moves fit within longstanding policies that aim to both ensure Israel's defense and to advocate for protection of civilians in the year-old war in Gaza.

But current and former officials privately acknowledge that they are milestones that increase U.S. involvement in Israeli strategy even as Biden heads for the door.

Israel has frequently resisted U.S. advice and has caused political difficulties for the Biden administration, which faces pressure from some liberal activists in the Democratic Party to use U.S. leverage to rein in Israel.

Aaron David Miller, a senior fellow at the Carnegie Endowment for International Peace, said that the administration's carrot-and-stick approach "implies at a time when you might not think the administration is all that active … that they are clearly thinking and acting.”

But he cautioned that Washington is unlikely to scale back its military support for Israel if the conflict with Iran deepens.

“It is almost inconceivable to me as we approach the possibility of a severe and serious escalation – the Israeli response and what the Iranians will do in return – that this administration could consider anything like a serious restriction or conditioning of military systems,” he said.

White House spokesperson John Kirby told reporters on Tuesday that the letter was not "meant as a threat" but that it appears the Israelis are taking the issues seriously.

An Israeli official in Washington said: “The letter has been received and is being thoroughly reviewed by Israeli security officials."

Israel said Wednesday that 50 aid trucks were transferred to north Gaza from Jordan, a possible early result of the U.S. demands.

A DEADLINE TO INCREASE AID

Biden has prioritized Israel's defense since Hamas militants triggered the war by killing some 1,200 people, according to Israeli figures. He refused to halt weapons flows to Israel, except for 2,000-pound bombs, despite outcry by fellow Democrats as Israel's war in Gaza killed 42,000 people, according to Palestinian health authorities.

The administration in April demanded better protections for civilians and aid workers in Gaza, which U.S. officials say produced a temporary rise in aid flows into the territory.

But Sunday's letter appeared to be the clearest ultimatum yet to Netanyahu's government since the Gaza conflict began, outlining specific steps Israel must take within 30 days, including enabling a minimum of 350 trucks with aid to enter Gaza per day.

It raises the possibility of Washington making Israel ineligible to receive U.S. weapons over its restrictions on aid delivery, said John Ramming Chappell, advocacy and legal advisor at the Center for Civilians in Conflict.

"It is a small step towards a very significant change," he said.

Netanyahu convened an emergency meeting on Wednesday to discuss expanding humanitarian aid to Gaza, three officials who attended the discussion said, with aid likely to increase soon.

The decision to send the Terminal High Altitude Area Defense system, or THAAD, is a similarly major step, said former officials and analysts, in line with a strategy of offering the Israelis close military support with the aim of influencing how they conduct military operations.

A former defense official described the deployment as a "paradigm shift," given Israel's long-standing security doctrine to defend itself, by itself. It also raises the stakes, potentially, for the United States.

"The U.S. is putting actual U.S. 'skin in the game' by placing U.S. forces inside Israel, that only 2 weeks ago was on the receiving end of 180 Iranian ballistic missiles," the official said.

The Middle East has been on edge awaiting Israel's response to a missile attack earlier this month that Tehran carried out in retaliation for Israel's military escalation in Lebanon.

Biden has objected to any Israeli strike on Iran's nuclear sites and expressed concern about a strike on energy sites.

"This is probably a carrot to try to cajole the Israelis to not go big," said Thomas Karako, director of the missile defense project at the Center for Strategic and International Studies, referring to the possibility that Israel could choose to strike nuclear and other targets.

"And, you know, you don't send a multi-billion dollar asset without some strings attached."

The White House did not directly respond to a question on whether sending the THAAD to Israel may have been part of a deal for the Israelis to agree not to hit Iranian oil or nuclear sites.

Time is running short for the administration.

The 30 days Biden has given Israel to comply with its demands will run out after the Nov. 5 U.S. election, giving Netanyahu the ability to decide how fully he should comply, said Miller, especially if the Republican candidate with whom he is close, former President Donald Trump, defeats the Democrat, Vice President Kamala Harris.

“Netanyahu believes he is at the point of maximum leverage, and he may well be. You may have a new president-elect that is much more to his liking in a matter of weeks,” Miller added.