Rebels in eastern Ukraine appear to be successfully closing in on the government-held airport in Donetsk, a strategic victory for the pro-Russian separatists that further undermines a shaky ceasefire in the region.

Shelling has killed six people and wounded 15 others in the Ukraine rebel stronghold of Donetsk, the city council said.

Clashes broke out outside the main rebel-held city in eastern Ukraine, throwing the freshly forged ceasefire deal between government troops and Russian-backed separatists into further doubt.

Clashes have broken out outside the main rebel-held city in eastern Ukraine, throwing the freshly forged ceasefire agreement between government troops and Russian-backed separatists into further doubt.

The airport of a volatile eastern Ukrainian city has been closed, a day after troops mounted an offensive against pro-Russian forces that killed at least a dozen people.