The White House previously warned it would “run out of resources” for Kyiv “by the end of the year”.
ADVERTISEMENTThe United States announced on Wednesday it had released its last tranche of military aid for Ukraine.
The White House approved $250 million (€225 million) in support, but more will need fresh approval from Congress.
Negotiations between Republicans and Democrats have stalled.
Ukraine has warned it cannot fight Russia without further support from the West.
The Kremlin, for its part, has banked on waning Western aid as key to an eventual win in Ukraine.
“It is imperative that Congress act as soon as possible to advance our national security interests by helping Ukraine defend itself,” US Secretary of State Antony Blinken said in a statement on Wednesday.
The latest tranche of aid includes ammo for air defence systems and anti-tank weapons.
Congress' failure to approve new funds is another disappointment for Ukrainian President Volodymyr Zelenskyy, following the failure of Kyiv's summer counteroffensive and a renewed push by Russian forces.
The White House previously warned it would “run out of resources” for Ukraine “by the end of the year”.
Zelenskyy came to Washington in December - his third trip to the US capital in a year - to try to increase the pressure.
But almost two years after Moscow launched its grinding invasion questions around supporting Ukraine "as long as it takes" continue to grow.
Right-wing Republicans have conditioned their support of more US aid for Kyiv on tightening immigration policy at home.
Talks on this explosive issue did not end in time.
US lawmakers will return to the issue of aid on 8 January.
Republican and Democratic leaders of the Senate have said they intend to approve a new tranche of assistance, including military, humanitarian and economic aid.
It is in the House of Representatives, which must also approve these funds, that things become complicated.
Its new president, Republican Mike Johnson, is not opposed to extending US aid, but claims it is not sufficiently regulated.