Ukrainian President Volodymyr Zelenskiy met with lawmakers at the U.S. Capitol as Republican skeptics question whether Congress should approve a new round of aid for his country despite slow progress fighting Russian invaders.

After seeking to shore up international support at the United Nations, Zelenskiy came to Washington on a crosstown blitz that includes meetings with U.S. President Joe Biden and military leaders at the Pentagon and an address in the evening at the National Archives museum.

While Biden and most congressional leaders still support aid to Ukraine, and Biden's Democrats control the Senate, Zelenskiy will face a tougher crowd than when he visited Washington nine months ago.

Dressed in military green to reflect his status as a wartime leader, Zelenskiy met with leaders of the Republican-led House of Representatives and House national security committees.

He then entered the Capitol's Old Senate Chamber alongside Majority Leader Chuck Schumer, a Democrat, and top Republican Mitch McConnell, where he was to address the full U.S. Senate in a private session.

As Ukraine's military counteroffensive grinds on and Congress stages a bitter debate over spending ahead of a possible government shutdown, a growing chorus of Republicans have questioned the billions of dollars Washington has sent Kyiv for military, economic and humanitarian needs.

The U.S. has sent some $113 billion in security and humanitarian aid to help Zelenskiy's government since Russia invaded in February 2022.

Russia carried out its biggest missile attack in weeks across Ukraine on Thursday, pounding energy facilities in what officials said appeared to be the first salvo in a new air campaign against the Ukrainian power grid.

Zelenskiy on Wednesday pressed his case for financial help with some of America's best known billionaires who made their fortunes in industries ranging from finance to tech and sports.

Biden administration officials held a classified briefing for Congress on Wednesday evening, to push for an additional $24 billion, saying if Russian President Vladimir Putin was allowed to take control of Ukraine and pushed through to the border of NATO, the cost to the United States would be much higher.

But some Republicans were not convinced.

"If there's some path in victory in Ukraine, I didn't hear it today. And I also heard that there's going to be no end to the funding requests," Republican Senator Josh Hawley, a vocal critic of Ukraine aid, told reporters.

Biden will announce a new $325 million military aid package for Ukraine, which is expected to include the second tranche of cluster munitions fired by a 155 millimeter Howitzer cannon.

"If we allow Ukraine to be carved up, is the independence of any nation secure?" Biden asked world leaders at the United Nations on Tuesday.

Congress approved Ukraine assistance easily when both the Senate and House were controlled by Democrats. Zelenskiy, who has become a powerful advocate for his country, was greeted as a hero when he addressed a joint meeting of Congress in December.

Support in the Senate, both from Biden's fellow Democrats and Republicans, has remained strong.

"Our nation has a fundamental interest in Ukrainian victory and European security," Senate Republican Leader McConnell said on Wednesday in a speech criticizing Biden for acting too slowly to help Ukraine.

Solid majorities of Americans support providing weaponry to Ukraine to defend itself against Russia, Reuters/Ipsos polling shows.

But some of the Republicans who took narrow control of the House in January are questioning the wisdom of continuing to send funds to Kyiv. About a third of the House Republican caucus voted in July for a failed proposal to cut funding for Ukraine.

Republican Speaker Kevin McCarthy did not arrange a meeting on Thursday where Zelenskiy could make his case for continued assistance to the entire House, just a small meeting with himself and a few other leaders. McCarthy, who as speaker controls what legislation comes up for House votes, said Zelenskiy needed to convince him to back continued aid.

"Is Zelenskiy elected to Congress? Is he our president? I don't have to commit anything," McCarthy told reporters on Tuesday. "I have questions for him. Where's the accountability on the money we've already spent? What is the plan for victory? I think that's what the American public wants to know."