Vice President Joseph Biden made the commitment in his meeting with Prime Minister Laimdota Straujuma of Latvia at the White House, while the prime minister thanked U.S. for its support in the forms of sending paratroopers to his country for drills and joining other NATO members in boosting the bloc's air policing of the Baltic nations.

　　They agreed on the need for the U.S. and Europe to remain united in confronting Russia's "destabilizing actions" in eastern Ukraine and "its illegal occupation" of Crimea, the White House said in a readout of the meeting.

　　It said the duo also discussed the "critical importance" of boosting Europe's energy security through coordinated actions among European states so as to reduce the continent's dependence on Russian gas. They agreed that the Transatlantic Trade and Investment Partnership, over which negotiations are underway, would play a "pivotal role" in creating jobs and supporting economic growth on both sides of the Atlantic.

　　Both the U.S. and the European Union slapped fresh sanctions on more Russian officials and firms Monday, and threatened to target its key sectors of economy in the event of further destabilizing moves in eastern Ukraine.

　　Russia has rejected suggestions that it is orchestrating events in eastern Ukraine, insisting it has no plan to invade that vast region.