The latest attack comes in the run-up to the presidential election on Sunday, which rebels have vowed to disrupt.

It is unclear how many protesters were involved or what happened to the miners.

Ukraine’s coal industry gained media attention last week when the country’s richest man and coal magnate turned against the pro-Russian rebellion, ending months of neutrality.

The BBC said Rinat Akhmetov had publicly criticised the separatists for disrupting operations and urged his employees to protest at their workplaces until peace was restored.

According to The New York Times, Akhmetov has been organising his employees into patrols since Tuesday.

He wanted them to take back the port city of Mariupol, being held by separatists, pointing out that they would lose their export-dependent jobs if the region became an unrecognised splinter state.

Pro-Russian separatists took over government buildings in April and declared independence after a referendum on May 11 that was condemned by Kiev as well as western nations.