The White House has approved another tranche of US military aid to Ukraine worth some $250m (£195m).
The latest package includes air defence, artillery and small arms ammunition, and anti-tank weapons, US officials say.
But it marks the last funding available without fresh approval from Congress, where talks have stalled. Ukraine has warned that the war effort and its public finances are at risk if further Western aid is not forthcoming.
Amid a stalled counter-offensive in the east of the country and a little-changed line of control, Ukrainian officials are facing the prospect of a slowdown in aid from allies in Washington and Europe. Although the Ukraine war effort has broad support in the US Congress, an agreement on further arms has been stopped by Republicans who insist that tougher security measures on the US-Mexico border must be part of any military aid deal.
An emergency spending measure that would have provided $50bn for Ukraine and $14bn for Israel was defeated in the Senate earlier this month, with every Republican voting against it - along with Bernie Sanders, an independent who usually votes with Democrats but has expressed concerns about Israel's war against Hamas.
A subsequent visit by Ukrainian President Volodymyr Zelensky failed to sway lawmakers.
Wednesday's announcement will see the weapons pulled from existing Pentagon stocks, a move which does not need Congressional approval.
Secretary of State Antony Blinken said in a statement announcing the aid package that it was "imperative that Congress act swiftly, as soon as possible, to advance our national security interests by helping Ukraine defend itself and secure its future".
"Our assistance has been critical to supporting our Ukrainian partners as they defend their country and their freedom against Russia's aggression," he added.
Earlier this month a €50bn EU aid package for Ukraine was blocked by Hungary.
Ukraine is facing a $43bn budget deficit and officials say they may have to delay salaries and pensions for government employees if further aid from the West does not come soon.
"The support of partners is extremely critical," Ukraine's Deputy Prime Minister Yulia Svyrydenko, who also serves as the country's economy minister, said in an interview with the Financial Times on Wednesday. "We need it urgently."
The newspaper reported that talks were progressing on a smaller aid package that would not need Hungary's approval, which could be taken up in early February.
As funding has slowed from Ukraine's Western allies, Russian forces have continued to fight in the east of the country, where they seized a key town on Tuesday.
Russian Defence Minister Sergei Shoigu said his troops took Mariinka in eastern Ukraine after Ukrainian forces pulled back. The town has been at the forefront of fighting for over a year.