President Joe Biden on Saturday told Ukrainian counterpart Volodymyr Zelenskyy that he is "confident" the US Congress will renew war aid, but added that without American help Kyiv could lose further territory to Russian advances.
"I spoke with Zelenskyy this afternoon to let him know that I was confident we're going to get that money," Biden told reporters after attending church in Delaware.
Failure by U.S. lawmakers to approve new funding for military aid to Kyiv would be "absurd" and "unethical," he said, adding: "I'm going to fight to get them the ammunition they need."
The leaders spoke hours after Russia captured the eastern Ukrainian stronghold of Avdiivka, a major symbolic victory for Russian President Vladimir Putin.
Avdiivka, now mostly destroyed, had been a symbol of Ukraine's determined resistance to Russian aggression since 2014.
The White House said in a statement the Ukrainian withdrawal from the town came "after Ukrainian soldiers had to ration ammunition due to dwindling supplies as a result of congressional inaction, resulting in Russia's first notable gains in months."
Biden told reporters he is not confident another Ukrainian city won't fall to Russian forces without an infusion of U.S. aid.
"I'm not. I'm not. No one can be," he said.
With existing U.S. funding already dried up, former president Donald Trump's allies in the House of Representatives have been stalling $60 billion in military aid.
Trump, the likely Republican nominee in the November presidential election, opposes helping Kyiv and recently used his sway to kill a U.S. border reform bill that would have also authorized additional aid to Ukraine.
In a post on Telegram following the phone call, Zelenskyy said: "I am glad that I can count on the full support of the American president. We also believe in the wise decision of the U.S. Congress."
The statements of U.S. support came as Vice President Kamala Harris and Secretary of State Antony Blinken were scrambling to reassure Western allies at the Munich Security Conference that Washington's support of Kyiv's war effort against the Russian invasion would continue.
Speaking in Munich earlier Saturday alongside Zelenskyy, Harris said: "As it relates to our support for Ukraine, we must be unwavering and we cannot play political games."