U.S. Vice President Joe Biden has said the United States will work with allies to "impose further costs on Russia" if Moscow fails to use its influence to stop separatist violence in eastern Ukraine.
The White House says Biden made the comment to Ukrainian President Petro Poroshenko in a telephone conversation on June 18.
Biden said Russia has failed to stop sending weapons and militants across the border.
Biden also commended Poroshenko for his commitment to move ahead with his peace plan and for other measures to unify the crisis-ridden country.
The new president of Ukraine is proposing a unilateral cease-fire after two months of fighting and promises a safe exit for pro-Russian armed separatists.
In related news, Poroshenko nominated Pavlo Klimkin, a pro-European diplomat now serving as ambassador to Germany, for foreign minister.
Based on reporting by AP and Reuters