Tens of billions of dollars in US aid has been sent to Ukraine since the invasion nearly two years ago -- but many Republican lawmakers have grown reluctant to keep supporting Kyiv, saying it lacks a clear end game as the fighting against President Vladimir Putin's forces grinds on.

Stoltenberg and Austin -- who has spearheaded the push for international military support for Kyiv -- met at the Pentagon, with top US military officer General Charles "CQ" Brown and other officials also in attendance.

President Joe Biden has asked Congress to approve $61 billion in new aid to Ukraine.

But the talks have bogged down as Republican lawmakers -- furious over record flows of migrants over the US border with Mexico -- demand major changes in immigration and border control policy in exchange for approving more money for Ukraine.

Stoltenberg said on Fox News the previous day that the agreement being negotiated in the US Congress is "a good deal."

US aid to Ukraine has been just a fraction of the Pentagon budget, and yet "we have been able to destroy and degrade the Russian army substantially," Stoltenberg said, adding: "And therefore we should continue to do so."

The assistance for Kyiv also helps American workers, because the money is used to buy weapons made in the United States, the NATO chief said.

Stoltenberg was due to meet with Secretary of State Antony Blinken and national security advisor Jake Sullivan later on Monday.

On Tuesday he is scheduled to meet Republican and Democratic lawmakers involved in the Ukraine aid debate.

Donald Trump, the likely Republican candidate in the November presidential election, and who has often praised Putin, is urging Republican lawmakers to reject the immigration accord being negotiated in Congress -- which would also torpedo aid for Ukraine.