U.S. disturbed by reports of Russian separatist attacks in Ukraine

WASHINGTON (Reuters) - The United States is disturbed by reports of combined Russian-separatist attacks in eastern Ukraine, the State Department said on Wednesday. State Department spokeswoman Marie Harf said such attacks were unacceptable and could lead to additional costs for Russia. "Russia bears direct responsibility for preventing these attacks and implementing a cease-fire," she said at a news briefing. Ukrainian troops and pro-Russian separatists on Wednesday fought their first serious battles in months and Ukraine's defense minister said an attempt by rebels to take the eastern town of Maryinka had been thwarted. (Editing by Bill Trott)