WASHINGTON, United States - The US government on Wednesday announced what it said was the last remaining package of weapons available for Ukraine under existing authorization, with Congress now needing to decide whether to keep supporting Kyiv's battle against Russian invasion.

A Ukrainian serviceman holds a MANPADS (Man-Portable Air-Defence Systems) "Stinger" anti-aircraft weapon as they scan for possible air targets, onboard a Maritime Guard of the State Border Service of Ukraine boat as it patrols in the northwestern part of the Black Sea on December 18, 2023, amid the Russian invasion of Ukraine. This boat is part of Kyiv's strategy aimed at keeping the Russian military fleet away from the Ukrainian coast, with the key mission of securing the corridor set up since August between Ukrainian ports in the Odessa region and the Bosphorus Strait, after Moscow slammed the door on an international grain agreement. (Photo by Anatolii Stepanov / AFP)

"The year's final package" includes air-defense and artillery munitions, the State Department said in a statement. It added that Congress, where Republicans are split on supporting Ukraine, should "act swiftly" to renew the flow.

President Joe Biden has made backing Ukraine a priority and US weapons and financial assistance have been crucial in helping the pro-Western country battle against a far larger attacking Russian force.

However, right-wing Republicans have led a push to halt the effort, refusing to authorize new budget outlays if the Democrats don't first agree to sweeping, tough new measures against illegal migration over the US southern border.

The final tranche of aid is worth up to $250 million and includes "air-defense munitions, other air-defense system components, additional ammunition for high mobility artillery rocket systems, 155mm and 105mm artillery ammunition, anti-armor munitions, and over 15 million rounds of ammunition," the State Department said.

The statement underlined the US-led coalition helping Ukraine, noting that "more than 50 countries" are involved.

"It is imperative that Congress act swiftly, as soon as possible, to advance our national security interests by helping Ukraine defend itself and secure its future," it said.

In Kyiv, Ukrainian presidential aide Andriy Yermak welcomed the aid.

"Thank you for your help. We will win," Yermak wrote on X, formerly known as Twitter.

A week ago, White House National Security Council spokesman John Kirby made clear that the upcoming drawdown of US military aid would be the last available, leaving "no more replenishment authority."

"We're going to need Congress to act without delay," he said.

Democrats in the Senate, where they hold a narrow majority, tried to push Republicans in December for a last-minute deal, but with little progress the two parties left for the end-of-year holidays.

Congress reconvenes on January 8.

However, finding agreement on immigration -- one of the most complex and longest-running headaches in US politics -- is expected to be difficult in the Senate.

Even then, a deal would have to be approved in the House of Representatives where Republicans -- dominated by a hard-right faction -- hold their own narrow majority.