Vice President Biden (Eric Thayer/Reuters)

Vice President Biden met with Poland's president on Tuesday and assured him that the United States remains more than capable of stepping up militarily if Russia's aggression were to spread to NATO allies.

“You have an ally whose (defense) budget is larger than the next 10 nations in the world combined, so don’t worry about where we are," Biden told President Bronislaw Komorowski during a visit to Poland.

Biden's comment came after Komorowski noted that Russia has recently multiplied its defense budget but that many NATO countries had cut theirs. The North American Treaty Organization (NATO) includes Poland and other neighbors of Ukraine, but not Ukraine itself.

NATO Article 5 states that if one NATO country is attacked, it constitutes an attack on all of them and that all of them must assist in responding.

The vice president also repeated the Obama administration's position that Russia's annexation of Crimea is illegal. He said Russia needs to let Ukraine decide its own future.

“Those that bet instead on aggression and fear-mongering are bound to fail,” Biden said.

Correction: The post initially said Biden was referring to the situation in Ukraine, not in NATO countries. It has been updated.