President Joe Biden told President Volodymyr Zelensky on Tuesday that the United States will not abandon Ukraine in its desperate fight against Russia, even as Republicans signaled opposition to extending US war funding.

Standing alongside the Ukrainian leader at a White House press conference, Biden vowed: "I will not walk away from Ukraine and neither will the American people."

And he said that allowing a Ukrainian defeat would mean Russian President Vladimir Putin "and would-be aggressors everywhere will be emboldened."

Zelensky, who spent the morning talking to Republicans and Democrats in Congress, signaled cautious optimism that the stalled US aid flow will restart.

"I got the signals. They were more than positive. But we know that we have to separate words and particular results. Therefore we will count on particular results," Zelensky said.

But the united front at the White House contrasted with growing division up on Capitol Hill, where leading Republicans are insisting that renewing Ukraine aid will depend on Democrats first agreeing to major immigration reforms — and even questioning whether the war against Russian invasion should continue.

As Moscow claimed fresh battlefield advances and predicted any new assistance for Kyiv would be a "fiasco," Republican House Speaker Mike Johnson expressed little enthusiasm for approving Biden's request for $60 billion in new assistance.

"What the Biden administration seems to be asking for is billions of additional dollars with no appropriate oversight, no clear strategy to win, and none of the answers that I think the American people are owed," Johnson told reporters after meeting Zelensky.

Republican Senator JD Vance — who is close to the party's leader and likely 2024 presidential candidate, Donald Trump — said on social media that Zelensky was "gross" for pressuring the Senate.

Russia pounds Ukraine

The Kremlin echoed Republican arguments, scoffing at the impact of US support.

"It is important for everyone to understand: the tens of billions of dollars pumped into Ukraine did not help it gain success on the battlefield," Kremlin spokesman Dmitry Peskov said Tuesday.

And Russia said it was pressing ahead on the ground, just as Ukraine's freezing winter deepens and Moscow's air attacks on Ukraine's cities increase.

Ukraine said Russia had launched a "massive offensive" with armored vehicles in another part of the front near Avdiivka in the east. 

In a blow felt by civilians behind the frontlines, Ukraine's main mobile operator said it had been paralyzed by a "powerful hacker attack."

Huge Russian losses

The United States said that in reality, Russia is paying an extraordinary price for small gains, with some 315,000 Russian troops killed or wounded in Ukraine since the war began in February 2022. 

Russian forces have also lost some 2,200 of the 3,500 tanks they had before the start of the conflict, according to a declassified US intelligence assessment shared with Congress.

The White House said Russia had suffered more than 13,000 dead and wounded in the east of Ukraine just since October.

But "Russia seems to believe that a military deadlock through the winter will drain Western support for Ukraine and ultimately give Russia the advantage despite Russian losses," National Security Council spokeswoman Adrienne Watson said.

As the United States ponders its future Ukraine policy, Polish Prime Minister-designate Donald Tusk called for "full mobilization on the part of the free world, the West, in support of Ukraine."