An "anti-terrorist operation" against pro-Russian separatists has begun, acting Ukrainian President Oleksander Turchynov announced Tuesday.
Pro-Russian rebels have been seizing buildings across Ukraine’s eastern provinces, a major industrial area. Meanwhile, thousands of Russian troops are deployed along the borders, according to BBC.
The ["anti-terrorist"] operation began in the "north of Donetsk Region," he told parliament, and was being conducted "stage by stage, in a responsible... manner".
Ukrainian armored vehicles could be seen massing on Monday as separatist militants braced for an attack.
The U.S. and Russian presidents have discussed the crisis by telephone.
Barack Obama urged Vladimir Putin to use his influence to make separatists in Donetsk and other parts of eastern Ukraine stand down.
Putin denied that Russia was intervening in the crisis.
