ISIS fighters have released the first of the 170 cement workers kidnapped from just outside Damascus - contradicting government claims that they had been executed.

Extremists seized the labourers from an area close to the town of Dumeir, northeast of the capital, earlier this week.

The kidnapping sparked a war of words between the two sides - with the jihadi group's media arm saying the workers were unhurt, while the state's military claimed they had been massacred in their dozens.

Now the British-based Syrian Observatory for Human Rights monitoring group has stepped in, saying local municipality officials in two nearby towns managed to secure an agreement for IS to release 170 workers it had been holding since Wednesday.

ISIS fighters have reportedly executed 175 of the 300 kidnapped cement workers outside the Syrian capital Damascus, according to the state's military (file picture)

The workers and contractors of Al Badia Cement company were taken from near the town of Dumeir

The workers and contractors of Al Badia Cement company were taken from near the town of Dumeir and their employer had lost all contact with them, the industry ministry is quoted as saying.

Earlier reports claimed a source in the company told state-run news agency SANA that there has been no success in efforts to establish contact with any of the workers.

SANA said 'employees and executives of the Al-Badia cement factory' were abducted by the jihadists, after local residents reported that at least 250 workers at the plant had been missing since Monday.

'The company has informed the industry ministry that it hasn't been able to make contact with kidnapped individuals,' SANA said.

A factory administrator told AFP that the factory workers have been unreachable since Monday.

'We haven't been able to reach our family members since noon on Monday after an attack by Daesh [Arabic derogatory term for ISIS] on the factory. We have no information about where they are,' a resident of the town of Dmeir said yesterday.

Mass abductions have taken place on occasion in Syria during the country's devastating civil war, now in its sixth year, most often of religious minorities such as Christians.

The abduction came as fighting with ISIS militants raged in northern Syria on Thursday. Syrian opposition fighters have advanced on strongholds of the terror group, including the ISIS-held town of al-Rai in northern Aleppo along the border with Turkey.

Earlier this week, ISIS fighters launched attacks on government-held areas near Damascus in what a Syrian source said appeared to be a response to the group's loss of ground elsewhere.

The group said in a statement it had attacked the Tishrin power station, 30 miles northeast of the capital. The Syrian military source acknowledged the group had staged assaults, but said all those who took part had been killed.

Earlier this week, ISIS fighters launched attacks on government-held areas near Damascus (pictured) in what a Syrian source said appeared to be a response to the group's loss of ground elsewhere

Syrian and allied forces backed by Russian air strikes have forced ISIS militants out of the town of al-Qaryatain, which lies between Damascus and the ancient city of Palymrya, itself recaptured by the government last week.

ISIS has also been losing ground to US-allied Kurdish forces in northern Syria, and in recent days to Turkish-backed rebel groups fighting a separate battle against the group north of Aleppo.

The Syrian source said Tuesday night's attacks outside Damascus appeared to be the jihadist group's response to its reverses around Palymra.

ISIS attackers, using five bomb-laden cars, also struck military positions near the Dumeir military airport 25 miles northeast of Damascus, killing 12 soldiers, the Syrian Observatory for Human Rights said.

ISIS claimed the bombings in an online statement, saying it carried out a suicide attack on government forces which were moving north from the military airport.

Government forces responded with shelling and air strikes around the Dumeir area, which is held by a rebel group sympathetic to ISIS, the Observatory said.

It added that the strikes have killed at least 15 civilians there, including four young girls from the same family, and that around 15 Islamic State fighters, as well as the drivers of its five bomb-laden cars, died in the clashes.