The United States will work on greater diversification of energy sources in the Baltics and may consider rotating units of its ground and naval forces through the region for training exercises, U.S. Vice President Joe Biden said on Tuesday.

Biden, who was speaking after meeting Estonian President Toomas Hendrik Ilves in the Polish capital, also said that his country remains committed to NATO's pledge to help member states if military action is taken against them.

Ilves said during a joint news conference with Biden that the European Union's response to Russia's intervention in Ukraine must be more robust and "should not be about the price of gas".