BEIRUT -- The Islamic State group has released most of the 300 cement workers it abducted near Damascus after questioning them to find out who were Muslims and killing four who were members of the minority Druze sect, a Syrian opposition monitoring group and a news agency linked to the extremists reported Saturday.

The reports came two days after IS abducted the cement workers and contractors from al-Badia Cement Company in Dumeir, just northeast of the capital, after a surprise attack on government forces.

The Britain-based Syrian Observatory for Human Rights said all those abducted have been released except for 30 people who were guards at the cement factory. It said the fate of the 30 is unknown.

The IS-affiliated Aamaq news agency said most of the 300 were released after questioning to determine their religion and whether they support the government. It said four workers who belonged to the minority Druze sect were killed and 20 pro-government gunmen are still being held.

The Druze, a 10th century offshoot of Shiite Islam, made up about 5 per cent of Syria's pre-war population of 23 million people. Lebanon and Israel also have large Druze communities.

IS, a Sunni Muslim extremist group, considers all Shiites to be heretics deserving death.

Aamaq also released a video from inside the cement plant, about 45 kilometres northeast of Damascus, showing trucks and bulldozers in the sprawling facility. Some fighters could be seen inside.

Government forces and insurgents meanwhile clashed near Handarat, just north of the northern city of Aleppo, Syria's largest, activists said. In the western part of Aleppo province, troops backed by Lebanon's Hezbollah fighters battled militants in Khan Touman and al-Ais, where insurgents last week killed more than two dozen Lebanese militants and government forces, according to activists and state media.

Elsewhere in northern Syria, a mine left behind by IS near the Kurdish town of Kobani killed at least four children and wounded several others late Friday. The Observatory said four children were killed and six wounded when the mine exploded in the village of Darb Hassan. State news agency SANA said six children were killed.

Kobani-based Kurdish official Idriss Naasan told The Associated Press that the children were shepherds who took their sheep and goats to graze in Darb Hassan on Friday. When they opened the door to a house, the mine exploded, killing four children and wounding the rest. He added that one is believed to have died of his wounds later.

Also in Syria's north, a senior official with al-Qaida's local branch appeared in a video during which he denied reports by state media that he was killed in the northwestern province of Idlib. The Observatory also reported that Sheikh Abdullah al-Mheisny was not harmed.

"I will remain a thorn in your throat and my happiest day will be when I get martyred," al-Mheisny said in the video. The militant was wounded by a Russian airstrike in December in Latakia province.

A Saudi citizen, al-Mheisny had been fighting in northern Syria for months, serving both as a senior religious and military commander with the al-Qaida branch, known as the Nusra Front.

Several top Nusra Front commanders have been recently killed in Syria by U.S. airstrikes.