"They've got to meet the same standards. So we're not going to make it easy," the US president told reporters near Washington.

The comments come before NATO leaders are set to meet in Lithuania next month.

In a symbolic step, alliance leaders are aiming to hold a first session of a NATO-Ukraine Council with President Volodymyr Zelensky in the Lithuanian capital of Vilnius, the alliance's chief Jens Stoltenberg said Friday in Brussels.

The meeting will give Kyiv a more equal seat at the table "to consult and decide on security issues," Stoltenberg said

But Stoltenberg added that though NATO will tighten political ties with Ukraine at the summit, there will be no talk of membership for Kyiv.

"We're not going to discuss an invitation at the Vilnius Summit, but how we can move Ukraine closer to NATO," Stoltenberg said.

"I'm confident that we will find a good solution and consensus."

NATO nations in eastern Europe have pushed for a better roadmap for Ukraine to obtain membership, but key allies like the United States and Germany have been reluctant to go much beyond a vague 2014 pledge that Kyiv will join one day.

German Defense Minister Boris Pistorius, however, had suggested Friday it was possible some requirements for membership could be eased if Ukraine was eventually ready to join.

NATO countries have already supplied weaponry worth tens of billions of dollars to Ukraine since Moscow launched its all-out invasion last February.

Yet some leaders in NATO worry that expanding membership to Ukraine would increase the chance of the alliance confronting Russia directly in a war.

Finland became NATO's 31st member in April, while Sweden's application to join the alliance has been stalled by Turkey. Ankara accuses Sweden of harboring Kurdish militants that it considers terrorists.

Biden was also asked Saturday about Russian President Vladimir Putin's assertions that Moscow had deployed nuclear arms within close ally and neighbor Belarus.

"I've commented on that many times. It's totally irresponsible," Biden told reporters at a military base near Washington, on his way to speak in Philadelphia.

The president's comments echoed sentiments from Secretary of State Antony Blinken, who a day earlier had called Belarus' choice to accept the weapons "provocative."