Washington DC - Ukrainian President Volodymyr Zelensky pleaded Tuesday in Washington for continued US military aid, but the Republican House speaker poured cold water on the desperate bid for help.

As Moscow claimed fresh battlefield advances and predicted any fresh assistance for Kyiv would be a "fiasco," Zelensky's attempt to keep Ukraine's main backer onside crashed into the realities of a bitter domestic political divide.

Republican House Speaker Mike Johnson, the gatekeeper for any deal, insisted after meeting Zelensky that his party would not approve President Joe Biden's request for $60 billion in fresh assistance for Kyiv unless Democrats meet their demands on immigration.

"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.

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The Ukrainian president, who wore a black sweater with a small Ukrainian trident symbol and olive green military trousers, did not comment on his meeting with Johnson but said his talks with Senate leaders were "friendly and candid."

Zelensky (45) was later set to move to the White House for one-on-one talks with President Biden — who has been a firm supporter since Russia's February 2022 invasion — and a joint press conference.

Biden (81) invited Zelensky to Washington days after the White House warned that money for Ukraine will run out by the end of the year without a deal with Congress.

Republicans have refused to back down unless Biden agrees to measures on US-Mexico border security and immigration reform — one of the most intractable issues in US politics.

Senate Democratic Majority leader Chuck Schumer warned after meeting Zelensky that Ukraine needed the aid "quickly" to prevent Russian President Vladimir Putin's forces from vanquishing Ukraine.

The Kremlin scoffed at the impact of US support, echoing the arguments made by some senior Republicans who say that continuing the flood of weaponry to Ukraine would be futile after Kyiv's summer counteroffensive stalled.

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"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. "The tens of billions of dollars that Ukraine wants to be pumped with are also headed for the same fiasco."

Russia said it was pressing ahead on the ground just as Ukraine's freezing winter deepens.

"Our units have advanced significantly forward northeast of Novopokrovka," said the Moscow-installed head of the Russian-occupied Zaporizhzhia region, Yevgeny Balitsky.

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."

The disruptions make it impossible to send out air raid alerts, just as Ukraine is dealing with nightly Russian bombings. The White House said that, in reality, Russia is paying a heavy price for small gains, with more than 13,000 dead and wounded in the east 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, Kyiv's main European ally, Poland, urged global support.

Polish prime minister-designate Donald Tusk called for the "full mobilization on the part of the free world, the West, in support of Ukraine in this war." The message will likely be echoed loudly by Biden at the White House.

Republican senators last week blocked Biden's request for $106 billion in emergency aid primarily for Ukraine and Israel. Talks are ongoing behind the scenes on a deal that would make concessions to Republican demands for tough measures against illegal immigration in return for the Ukraine package.

However, Biden, who is seeking reelection next year, needs to thread a narrow passage between giving Republicans what they want and not alienating the left of his own party.