BEIRUT (REUTERS) - Islamic State in Iraq and Syria (ISIS) militants began releasing late on Friday some of the scores of cement plant workers they kidnapped north-east of Damascus this week, the Syrian Observatory for Human Rights monitoring group said.

Local municipality officials in two nearby towns managed to secure an agreement for ISIS to release 170 workers it had been holding since Wednesday, the Britain-based Observatory said.

ISIS seized the workers after launching an attack on Syrian government forces in the area where the cement plant is located, near the town of Dumeir.

Syrian state television said ISIS had kidnapped 300 workers and contractors.

The Observatory said 140 workers had fled before the fighters arrived.

ISIS' Amaq news agency said on Friday the group freed nearly 300 workers, but had executed four of them for being from the Druze minority.