Russia's Foreign Minister Sergei Lavrov on Monday insisted Moscow did not accept the departure of Syrian President Bashar Assad as a prerequisite for launching any peace process in the war-torn country.

Russia -- one of Assad's few remaining allies along with Iran -- has launched a fresh diplomatic push to find a way out of the four-year civil war that has cost some 240,000 lives.

The toll in Syrian government air strikes on a rebel-held town outside Damascus neared 100 Monday, as the U.N.'s humanitarian chief expressed horror and appealed for civilians to be protected.

Sunday's series of raids on the town of Douma, in the rebel bastion of Eastern Ghouta, was one of the bloodiest regime attacks in Syria's four-year war.

The death toll in Syrian government air strikes on a rebel-held town outside Damascus neared 100 on Monday, with U.N. officials expressing horror at the "unacceptable" attack.

Sunday's series of raids on the town of Douma, in the rebel bastion of Eastern Ghouta, was one of the bloodiest regime attacks in Syria's four-year war.

New United Nations humanitarian chief Stephen O'Brien held talks with Syria's foreign minister on Sunday during his first trip to Damascus since taking the top aid post.

O'Brien, who succeeded Valerie Amos in May, told Walid Muallem he was ready to work with the Syrian government to alleviate humanitarian suffering in the country, according to Syria's state news agency SANA.

Al-Qaida's Syrian affiliate Al-Nusra Front has freed several members of a U.S.-trained rebel force that it kidnapped two weeks ago, the Western-backed unit said in a statement.

In a statement circulating on social media, Division 30 said seven of its members had been freed by Al-Nusra after being captured in late July.

One Turkish soldier and three suspected members of the outlawed Kurdistan Workers' Party (PKK) were killed in eastern Turkey in new violence blamed on the Kurdish rebels, the state media said Sunday.

Fighting erupted in the early hours of Sunday near Kagizman town in eastern Kars province during a security sweep of the area, the official Anatolia news agency reported.

Democratic presidential hopeful Hillary Clinton returned fire Saturday at her Republican rival Jeb Bush's claim that a "premature" U.S. pullout from Iraq fueled the rise of the Islamic State group.

Clinton served as secretary of state under President Barack Obama during the rise of the self-proclaimed Islamic State (IS).

Scores of Syrian refugees who recently arrived on the Greek island of Kos began registering early Sunday on a ship sent by the government following tensions over a huge influx of arrivals.

The Eleftherios Venizelos, docked in Kos since Friday, will be moored for about two weeks, officials say.

Defected Colonel Abdullah Hussein al-Rifai, the so-called leader of the Free Syrian Army in Arsal and its outskirts, was shot dead Friday in the Lebanese border town.

State-run National News Agency said the shooting occurred in the town's square.

After talks with Moscow's top diplomat, Syria's main opposition group insisted Friday that Russia is "not clinging" to President Bashar Assad.

The head of Syria's National Coalition, Khaled Khoja, met Thursday with Russian Foreign Minister Sergei Lavrov as part of a fresh push by Moscow to find a way out of the four-year civil war that has cost some 240,000 lives.