WASHINGTON — The Biden administration on Monday sent Congress an urgent warning about the need to approve tens of billions of dollars in military and economic assistance to Ukraine, saying Kyiv’s war effort to defend itself from Russia’s invasion may grind to a halt without it.

In a letter to House and Senate leaders and released publicly, Office of Management and Budget Director Shalanda Young warned the U.S. will run out of funding to send weapons and assistance to Ukraine by the end of the year, saying that would “kneecap” Ukraine on the battlefield.

She added that the U.S. already has run out of money that it has used to prop up Ukraine’s economy, and “if Ukraine’s economy collapses, they will not be able to keep fighting, full stop.”

“We are out of money — and nearly out of time,” she wrote.

Biden has sought a nearly $106 billion aid package for Ukraine, Israel and other needs, but it has faced a difficult reception on Capitol Hill, where there is growing skepticism about the magnitude of assistance for Ukraine and where even Republicans supportive of the funding are insisting on U.S.-Mexico border policy changes to halt the flow of migrants as a condition for the assistance.

Meanwhile, the GOP-controlled House has passed a standalone assistance package for Israel, which is fighting a war with Hamas in Gaza, while the White House has maintained that all of the priorities must be met.

Congress already has allocated $111 billion to assist Ukraine, including $67 billion in military procurement funding, $27 billion for economic and civil assistance and $10 billion for humanitarian aid. Young wrote that all of it, other than about 3% of the military funding, had been depleted by mid-November.

The Biden administration has said it has slowed the pace of some military assistance to Kyiv in recent weeks to try to stretch supplies until Congress approves more funding.

“We are out of money to support Ukraine in this fight,” Young wrote. “This isn’t a next year problem. The time to help a democratic Ukraine fight against Russian aggression is right now. It is time for Congress to act.”

The letter followed a classified Capitol Hill briefing on Nov. 29 for the top House and Senate leaders on the need for the assistance. Defense and other national security officials briefed the “big four” congressional leaders as Congress is debating President Joe Biden’s nearly $106 billion funding package, which includes $61 billion for Ukraine but has become snared by Republican demands for U.S.-Mexico border security changes.

“They were clear that Ukraine needs the aid soon — and so does our military need the aid soon,” Senate Majority Leader Chuck Schumer told The Associated Press in an interview.