A 72-hour ceasefire came into effect Wednesday between Islamist groups and pro-regime forces, including Hizbullah, in flashpoint towns in northwest Syria and along the border with Lebanon, a resident and monitoring group said.

"We really noticed that it was relatively calm this morning," Mohammad, a resident of the flashpoint town of Zabadani near Lebanon's border, told AFP.

Syria's government is committing war crimes against besieged residents of Eastern Ghouta outside Damascus, with heavy aerial bombardment compounding the misery created by a regime blockade, Amnesty International said Wednesday.

In a new report, the rights group said some 163,000 people in the region were engaged in an "agonising struggle to survive."

The Islamic State group released 22 Assyrian Christians that it had abducted in northeastern Syria almost six months ago, activist groups said.

They were among more than 200 members of the Christian minority who were kidnapped by IS in February as it swept through the Khabur region in the northeastern Hasakeh province.

A major conservative Islamist rebel group in Syria announced its support on Tuesday for a joint U.S.-Turkish plan to establish a border zone free of the jihadist Islamic State group.

The powerful Ahrar al-Sham rebel faction said the IS-free zone, planned along a stretch of border in the northern province of Aleppo, "is in the interest of the Syrian people".

Saudi Arabia's foreign minister on Tuesday poured cold water on Russian calls to join forces with the Syrian authorities against Islamic State jihadists, insisting it would never work with President Bashar Assad. 

Moscow -- one of Assad's few remaining allies -- has called for coordination between the Syrian government and members of an international coalition fighting the extremist group, which controls swathes of territory in Syria and Iraq.

At least 25 Syrian rebels were killed overnight in an attack by Islamic State group fighters on an insurgent stronghold in Aleppo province, a monitor said on Tuesday.

Fighting lasted until dawn on Tuesday in Marea, one of the most significant rebel bastions in the divided province. The town sits on a road linking eastern Aleppo city and the border with Turkey.

Social Affairs Minister Rashid Derbas has said that Lebanon should benefit from a decision by al-Qaida-linked al-Nusra Front in Syria to withdraw from areas along the border with Turkey.

The move by al-Nusra Front came two weeks after Turkey began carrying out airstrikes against Islamic State group targets in Syria. Turkey also agreed to allow U.S. warplanes to use the strategic Incirlik Air Base for operations against IS in Syria.

Iran's Foreign Minister Mohammad Javad Zarif began a two-day visit to Lebanon on Tuesday by meeting Prime Minister Tammam Salam.

“We discussed cooperation between the two countries and bilateral ties,” said Zarif after the Grand Serail talks.

General Security has arrested three Syrians on suspicion of recruiting fighters and monitoring the activities of the Hizbullah-linked Resistance Brigades.

As Safir daily said Tuesday that Abu Khattab, one of the group's members, is a resident of the town of Shehim in Iqlim al-Kharroub. He left Lebanon through the Arida border crossing in December 2012, heading to the Syrian city of Aleppo where he joined al-Qaida-linked al-Nusra Front.

The U.S. State Department on Monday welcomed the release of Syrian human rights activist Mazen Darwish, and demanded the immediate release of tens of thousands of people it said were being held without fair trials. 

The State Department called for all charges dropped against Darwish, the director of the Syrian Center for Media and Freedom of Expression (SCM) who was arrested in February 2012 along with two of his colleagues.