U.S. Vice President Joe Biden said Russia is on a "dark path" to isolation with its actions in Ukraine and that the United States will respond to any aggression against its NATO allies.
Biden made the comments while in Lithuania, during a trip to reassure Baltic allies concerned about Russia's move to annex Ukraine's Crimea.
Biden met with the leaders of Lithuania and Latvia Wednesday after a visit to Poland on Tuesday. He reaffirmed the U.S. pledge to protect its NATO allies from attack.
The Baltic nations of Lithuania, Latvia and Estonia are NATO members. Ukraine is not.
WATCH: US Reassures Allies as Tensions Mount Along Russian Borders
The countries have condemned Russian President Vladimir Putin for moving to annex Ukraine's Crimea, and the White House announced a new round of sanctions will be put into place against Russia.
On Tuesday, Biden said the U.S. might conduct war games in the region and Washington has already added more fighter jets to patrol the airspace over the Baltics.
"The situation is alarming," Lithuanian President Dalia Grybauskaite said to Biden at the start of their meeting. Latvian President Andris Berzins also attended.
The Baltic states are also concerned about the economic impact of tensions with Russia. They worry Putin could retaliate through trade bans or by withholding natural gas.
Last week, Russia suspended food imports through Lithuania's major port in a move some viewed as an effort by Putin to exert political pressure.
Some information in this report was provided by Reuters.