Joe Biden/Ukraine aid
US President Joe Biden delivers remarks urging Congress to pass his national security supplement request, which includes funding to support Ukraine, in the Roosevelt Room of the White House. AFP

President Joe Biden urged feuding US lawmakers Wednesday to approve military aid for Kyiv, warning that Russian President Vladimir Putin would not stop with Ukraine and could even clash with NATO.

Democrat Biden said he was ready to make a "significant compromise" with Republicans who are blocking $60 billion in Ukraine assistance while they seek tough measures against migrants on the border with Mexico.

"This cannot wait," Biden said in an impassioned, televised address at the White House.

"Frankly, I think it's stunning that we've gotten to this point in the first place, where Republicans in Congress are willing to give Putin the greatest gift he could hope for."

Biden was speaking after a video summit with Ukrainian President Volodymyr Zelensky and the leaders of G7 nations to discuss how to shore up western aid for Kyiv as it battles the invasion Russia launched in February 2022.

Zelensky warned the leaders that Moscow was counting on western unity to "collapse" next year and said Russia had ramped up pressure on the front lines of the war.

Talking in the Roosevelt Room near a portrait of World War II-era president Franklin D. Roosevelt, Biden gave a stark warning that if Putin won in Ukraine "he won't stop there."

"If he keeps going and then he attacks a NATO ally... then we'll have something that we don't seek and that we don't have today: American troops fighting Russian troops."

Ukraine's Zelensky unexpectedly canceled a planned videolink appearance with US senators on Tuesday in which he was to have appealed for continued funding.

The Senate is due to hold a procedural vote later Wednesday on an emergency $106 billion package that includes the assistance for Kyiv plus aid for Israel's war with Hamas, and for border security.

But Senate Republicans are making their support for additional Ukraine funding contingent on Biden's Democrats accepting reforms to the asylum system and tightened border security -- measures the Democrats have already rejected.

The debate has become increasingly bad-tempered with some Republican senators walking out of a classified briefing on Tuesday.

Even as he castigated them for their "extreme" position, Biden held out an olive branch to Republicans on the issue.

"I am willing to make significant compromises on the border," Biden said on Wednesday. "I'm ready to change policy."

The White House has warned that the United States would run out of money for more Ukraine aid by the end of the year if Congress did not approve fresh funds for Kyiv.

The US State Department separately announced a stopgap $175 million tranche of new aid for Ukraine on Wednesday including prized HIMARS rockets, shells, missiles and ammunition.

The funding row underscores signs that Western support for Ukraine is fraying just as Kyiv's counteroffensive falters and Putin's forces push for new gains.

Ukraine's offensive has employed billions of dollars' worth of Western weapons but the front lines have barely shifted in more than a year and Russian attacks along the front have intensified.

Putin last week signed a decree to boost Russian forces by 15 percent to support his invasion of Ukraine, increasing the army by some 170,000 people.

Moscow has recently given signs about a possible peace deal, although one involving a shrunken, neutral Ukraine that would be impossible to swallow for Zelensky.

Russia's foreign ministry told AFP this week that a lasting peace with Ukraine can only happen if the West stops sending arms and if Kyiv accepts "new territorial realities."

Ministry spokeswoman Maria Zakharova said for any deal to happen, Ukraine should have neutral status and the rights of Russian-speaking residents should be protected.

She added that "at the moment, we do not see the political will for peace either in Kyiv or in the West."