Obama once again voiced U.S. support for the sovereignty and territorial integrity of Ukraine, a White House statement said.
"Human casualties grow as a result of military actions," the U.S. president said.
"Putin has a chance to take the opportunity of talks between Russia, France, Germany and Ukraine in order to achieve a peaceful resolution of the conflict," he said.
Obama also stressed the importance of reaching a peaceful resolution and the implementation of the Minsk agreements.
"However, if Russia continues its aggressive actions in Ukraine, including sending its troops, weapons and funding to support the separatists, the price for such Russian actions will grow," he said, according to the statement on the White House Web site.