U.S. President Barack Obama called six world leaders on Saturday to discuss the ongoing crisis in Ukraine, the White House said.

Obama spoke separately with British Prime Minister David Cameron, French President Francois Hollande and Italian Prime Minister Matteo Renzi about Ukraine, according to a readout from the White House.

Obama welcomed the "strong, unified" stance of the United States and the European Union on Russian actions in Ukraine, including the conclusions of the European Council.

The European Union on Thursday decided to conduct targeted measures against Russia as a result of the Ukraine crisis, calling for solution to the crisis through negotiations between Ukraine and Russia.

Obama, who is on a weekend vacation with his family in Florida, also held a conference call with the presidents of Lithuania, Latvia and Estonia. He reaffirmed the United States' "unwavering commitment" to its collective defense commitments under the North Atlantic Treaty and "enduring support for the security and democracy" of the Baltic countries.

It was the first time Obama has spoken with the leaders of the three Baltic states about the crisis. The three countries are NATO members with strong economic ties to Russia.

U.S. Defense Secretary Chuck Hagel said Wednesday that the U.S. plans to expand military cooperation with Poland and Baltic states to show "support" for its allies amid crisis in Ukraine.

The U.S. has accused Russia of "violating" Ukraine's sovereignty and territorial integrity as well the international law by its military intervention in Crimea, while calling for withdrawing its troops and starting talks with Ukrainian interim government to find a diplomatic solution. Washington has also imposed visa bans and financial sanctions on a number of Ukrainians and Russians it claims responsible for the crisis.