WASHINGTON, United States - The White House issued a dire warning Monday that US aid for Ukraine will run out by the end of the year, adding that Russian President Vladimir Putin could win the war if Congress fails to agree fresh funding.

(AFP Photo)

President Joe Biden's budget director, Shalanda Young, said in a blunt letter to Republican House Speaker Mike Johnson that if military assistance dries up it would "kneecap" Kyiv's fight against the Russian invasion.

Democrat Biden asked Congress in October for a huge $106 billion national security package including military assistance for Ukraine and for Israel's war against Hamas, but the funding has been mired in divisions on Capitol Hill.

"There is no magical pot of funding available to meet this moment. We are out of money -- and nearly out of time," wrote Young.

"Cutting off the flow of US weapons and equipment will kneecap Ukraine on the battlefield, not only putting at risk the gains Ukraine has made, but increasing the likelihood of Russian military victories."

National Security Advisory Jake Sullivan went further, suggesting that voting against aid for Ukraine was effectively voting to make it easier for Russia to succeed.

"Congress has to decide whether to continue to support the fight for freedom in Ukraine...or whether Congress will ignore the lessons we've learned from history and let Putin prevail," Sullivan told reporters at the White House.

"It is that simple. It is that stark a choice."

- 'Judgment of history' -

Ukraine has been desperately pushing for more western aid as Russian forces step up attacks in the winter after Kyiv's counteroffensive failed over the summer.

But Congress has been paralyzed for months by Republican infighting, with hard-right lawmakers particularly opposing any further assistance for Kyiv as the war drags into its third year.

Speaker Johnson, who took office in October after his predecessor was ousted in a right-wing coup, gave the White House letter a cool response.

"The Biden administration has failed to substantively address any of my conference's legitimate concerns about the lack of a clear strategy in Ukraine," Johnson said on X, formerly Twitter, on Monday.

Johnson also repeated the Republicans' insistence on tying any Ukraine aid to changes in US policy on the southern border with Mexico, as the number of migrant arrivals surges.

Casting Putin and Hamas as twin forces trying to "annihilate" neighboring democracies, Biden has sought to tie $61 billion for Ukraine with $14 billion for Israel in the aid package he demanded in October, along with funding for the border.

Democratic US Senate Majority Leader Chuck Schumer said the "judgment of history will be harsh indeed" if Congress failed to act.

He added that the issue was not genuine but that Republicans had "injected partisan and extreme immigration measures into the debate."

"You can bet Vladimir Putin is watching. Hamas is watching. Iran, President Xi, North Korea -- all our adversaries, they are watching closely."

- Putin 'won't make peace' -

Ukraine's frontline has largely remained static for the last year despite a massive push by Ukrainian forces this summer with Western military hardware.

The United States has already allocated $111 billion for Ukraine since Russia invaded in February 2022, including $67 billion for military procurement, Young said.

European countries are also facing challenges in securing funding for Ukraine as fatigue with the war sets in.

Fears are growing in Washington that Putin may be content to sit out the situation until next year's US presidential election, a probable replay of 2020's contest between Biden and Donald Trump.

Polls show a growing number of voters saying the United States is doing too much to help Kyiv.

"I think my expectation is that Putin won't make peace or a meaningful peace before he sees the result of our election," a senior State Department official told reporters last week.

The official would not say why but Moscow is widely seen as favoring a return by Trump, who has praised the Russian leader and questioned US aid for Ukraine.