The Latest: Observer group: 21 pro-government gunmen killed

The Latest on developments in Syria (all times local):

2:50 p.m.

A Syria war monitoring group says 21 pro-government gunmen have been killed in clashes with the Islamic State group in southern Syria.

The Syrian Observatory for Human Rights says the fighters died in clashes with the militants Monday night in the Safaa region in the Syrian desert.

Government forces backed by local and regional militias have been battling the militants for weeks in the countryside north of Sweida since the militants ambushed the city and its environs in July.

The militants are holding some 30 civilians captive since kidnapping them in the assault. They are believed to be holding them in the Safaa area.

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1 p.m.

Turkey's president has urged the international community to act toward preventing a Syrian government offensive against Idlib, the last major rebel stronghold in Syria.

In an op-ed printed in the Wall Street Journal on Tuesday, Recep Tayyip Erdogan said the offensive on Idlib would "create serious humanitarian and security risks for Turkey, the rest of Europe and beyond."

His comments came days after Iran and Russia backed a military campaign in Idlib despite Turkey's pleas for a cease-fire.

Syrian Government forces, backed by Russia and Iran, have been massing troops for weeks in preparation for an attack.

Erdogan said the attack would amount to "indiscriminate attacks to wipe out its opposition and not a genuine or effective campaign against terrorism."

The Turkish president also said Russia and Iran had the responsibility to stop the humanitarian disaster.

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11:30 a.m.

A U.S.-backed Syrian fighting force says it has launched a campaign to clear the Islamic State group from its last pocket in northeast Syria.

The Syrian Democratic Forces says operations began on Monday to expel IS militants from the town of Hajin and surrounding villages on the northeast banks of the Euphrates River.

The SDF is supported by the U.S.-led international coalition against IS.

The Syrian Observatory for Human Rights monitoring group says coalition jets have bombed locations across the IS pocket in conjunction with the SDF ground offensive. The group says at least 23 IS fighters have been killed in the first 24 hours of battle.

The jihadist group today holds just a fraction of the territory it held at its 2014 peak.