Two plane-loads of U.S. military assistance arrived in Kyiv Sunday to boost Ukraine's defenses.
Officials say the shipment includes ammunition and shoulder-fired grenade launchers.
"Ukraine needs the necessary military weapons to defend itself," said Andrew Futey, president of the Ukrainian Congress Committee of America.
The U.S. and NATO allies are continuing to step in to help. President Biden's National Security Advisor Jake Sullivan warned Sunday on CNN that a Russian invasion of Ukraine could happen "any day now."
"We are prepared to continue to work on diplomacy," he said. "But we are also prepared to respond in a united and decisive way with our allies and partners should Russia proceed."
Sullivan's comments come a day after President Biden warned Russian President Vladimir Putin of "swift and severe costs" if he orders an invasion. And while Sullivan says it's hard to predict the day, he adds there has been an "acceleration" of Russian troop build-up.
"The way they have built up their forces makes it a distinct possibility that there will be major military action very soon," Sullivan said.
Pentagon Press Secretary John Kirby pointed to Russia's continued build up of forces along the Ukraine border. That number is now roughly 130,000.
"We have good sources of intelligence and they're telling us that things are sort of building now to some kind of crescendo opportunity for Mr. Putin," Kirby said.
President Biden has repeatedly warned American citizens in Ukraine to leave before it's potentially too late.
"The airports are still open. The railroads are still running. The highways are still open," Kirby continued. "There are plenty of opportunities for Americans to leave and they should take these warnings and advisories very seriously."