A coalition of U.S.-backed Kurdish militia and rebel groups has launched its first operation against territory controlled by the Islamic State jihadist group in northeast Syria, a spokesman said Saturday.

The Syrian Democratic Forces (SDF) were formed in mid-October as an alliance between the powerful Kurdish People's Protection Units (YPG) and other Syrian rebel groups.

At least 91 people, including 17 children, were killed on Friday in attacks on opposition strongholds in the north and outside Damascus, the Syrian Observatory for Human Rights said.

The deaths came as top diplomats from 17 countries, including Iran and Saudi Arabia, met for the first time in Vienna hoping to find a political solution to the conflict.

Turkey pressed on with its "war on terror" on Tuesday, just five days before the country goes to the polls, detaining dozens of Islamic State suspects and hitting Kurdish rebels across the border in Syria.

President Recep Tayyip Erdogan has been playing the security card in the run-up to Sunday's vote with tensions running high over the renewed Turkish conflict and a massive bomb attack blamed on IS jihadists.

Britain, France and Spain will soon present a draft resolution to the U.N. Security Council on stopping the Syrian regime from using barrel bombs, the French envoy said Thursday.

But it remains highly unlikely that Russia, Syria's ally, would support such a measure, which comes amid fierce Western criticism of Moscow's air war in Syria.

More than a quarter of a million people have been killed in Syria's brutal conflict since it began with anti-government protests over four years ago, a monitoring group said Friday.

The Syrian Observatory for Human Rights said it has documented the deaths of 250,124 people, including at least 74,426 civilians.

A doomed U.S. plan now on hold to train Syrian rebel fighters outside the country to fight the Islamic State was "nuts," former defense secretary Robert Gates said.

President Barack Obama's administration has suspended its $500 million train and equip effort in the latest embarrassment concerning a Syria strategy that has stumbled from one setback to the next.

Iran would consider sending fighters to key ally Syria if Damascus requests them, a senior Iranian official said Thursday on a visit to the war-torn country.

"If Syria makes a request (for Iranian forces), we will study the request and make a decision," said Alaedin Boroujerdi, the chairman of the Iranian parliament's national security and foreign policy committee.

The EU demanded Monday the "immediate" halt of Russian air strikes against moderate Syrian rebel groups and warned a lasting peace was impossible under Moscow-backed President Bashar Assad.

EU foreign policy chief Federica Mogherini called Russia's military intervention in Syria an unwelcome "game-changer" that jeopardized peace efforts and risked clashes with western aircraft targeting Islamic State jihadists.

An Iranian general killed in the Syrian city of Aleppo had taken part in 80 missions in the war-torn country, mourners were told at his funeral in Tehran on Sunday.

Hossein Hamedani of the Islamic Republic's Revolutionary Guards Corps became its highest-profile casualty of the effort to shore up Syrian President Bashar Assad when he died Thursday.

Islamic State group fighters advanced Friday to the outskirts of Syria's second city Aleppo, despite Moscow's announcement that its raids had killed hundreds of jihadists in just 24 hours. 

With Moscow in its 10th day of strikes, the United States announced it would halt its troubled program to build up Syrian rebel units to fight IS.