KIEV, Ukraine—Ukrainian officials said they were moving ahead with an operation against pro-Russian separatists in the country's east on Friday, seeking to isolate Slovyansk, the city at the heart of the insurgency, rather than confront militants head-on and risk civilian casualties.
There were few other immediate signs that what Kiev calls an antiterrorist operation had revved up, though a military helicopter exploded after being hit by a sniper shot while it was warming up.
President Vladimir Putin condemned the use of military force against civilians in a phone call with German Chancellor Angela Merkel, the Kremlin said, as his foreign minister reiterated warnings to Ukrainian leaders.
