President Biden said Monday that Ukraine had yet to meet standards required to join NATO but would receive the necessary support from the alliance amid rising tensions with Russia.

The president addressed his stance on Ukraine following a meeting with NATO leaders on the eve of his scheduled summit with Russian President Vladimir Putin, who has strongly opposed their potential membership with the alliance. Biden indicated Ukrainian leaders would need to deal with corruption within the government and combat the influence of powerful oligarchs to demonstrate their commitment to democratic values.

"It depends on whether they meet the criteria. The fact is, they still have to clean up corruption. The fact is, they still have to meet other criteria to get into the action plan. You know, school’s out on that question. It remains to be seen," Biden said. 

"In the meantime, we will do all we can to put Ukraine in a position to be able to continue to resist Russia’s physical aggression. It will not just depend on me whether or not we conclude that Ukraine can become part of NATO, it will depend on the alliance and how they vote," he added.

Earlier Monday, Ukrainian President Volodymyr Zelensky called on Biden to provide a "yes or no" answer as to whether he supported Ukraine’s entrance into NATO. Russia has long denied that it has an active military presence within Ukraine, though tensions have remained high in recent months as Russian troops massed near the border. 

Zelensky expressed disappointment that he was not able to meet with Biden ahead of his meeting with Putin on Wednesday in Geneva, Switzerland. In a phone call last week, Biden told the Ukrainian president that he would "stand up firmly" for Ukraine’s sovereignty during the Putin summit.

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At his press conference, Biden warned Russia against further aggression toward Ukraine.

"They have more to do, but that does not justify – the fact they have more to do – Russia taking aggressive action, either in the Donbas or on the sea or in any part of Ukraine. We’re going to put Ukraine in a position to be able to maintain their physical security," Biden said.

The Associated Press contributed to this report.