KRAMATORSK, Ukraine — A Ukrainian military helicopter was hit by rocket fire and exploded while on the ground on Friday at an airfield near the rebel-held eastern city of Slavyansk, the Defense Ministry said.

"According to a preliminary assessment, the explosion was the result of fire from a rocket-propelled grenade launcher," it said in a statement. There were no casualties, it said.

A senior security official earlier told a news briefing that the Mi-8 transport helicopter was hit in the fuel tank by a sniper bullet and that the pilot was injured.

A Reuters correspondent saw thick black smoke rising over the airfield and Ukrainian troops were barring access. Local residents said they had heard shooting and three explosions.