pro-russian separatist
A pro-Russian separatist guards a checkpoint outside Lysychansk in the Luhansk region of eastern Ukraine. Reuters

Pro-Russian rebels have fled their eastern stronghold of Slovyansk following heavy clashes in the eastern Ukrainian city, according to reports.

Most of the rebels and their senior commander left the city and moved into neighbouring Kramatorsk, according to the ITAR-TASS news agency.

The rebels reportedly left behind a small number of fighters ̵̶ mostly volunteers ̵̶ at roadblocks around the town.

"This morning, intelligence reported that Igor Girkin [also known as Igor Strelkov] and a substantial part of the rebels had fled Slovyansk," Ukraine's interior minister Arsen Avakov said.

He added: "An interior ministry's squadron has carried out a reconnaissance raid in Artyomovsk. The headquarters of the Donetsk People's Republic has been destroyed."

In a Facebook post Avakov also said that civilians were taking over roadblocks previously controlled by insurgents and are "carrying weapons and bulletproof vests abandoned by the rebels".

Pro-Russian separatists in eastern Ukraine and a spokesman for the Donetsk People's Republic denied the reports that they had fled the city.

Separatists seized the industrial city with a population of almost 120,000 people on 6 April. The following month, 30 rebels brought down a military helicopter killing 14 servicemen.

On Thursday, Ukrainian troops surrounded the village of Nikolayevka, near Slovyansk, clashing with rebel fighters.

On 1 July, Ukrainian President Petro Poroshenko announced the end of the ceasefire between pro-Kiev forces and separatists in the east of the country.

Just a few hours after the ceasefire was lifted, the Ukrainian army resumed fighting in the Luhansk region, on Ukraine's border with Russia .

Luhansk and Donetsk refused to recognise the legitimacy of the new Ukrainian government, following the country's regime change in February.

Both regions held referendums on seceding from Ukraine and declared themselves independent states.

In June, the self-proclaimed Donetsk People's Republic passed a constitutional law on confederation with the Luhansk People's Republic to form the Union of People's Republics.