The international talks in Vienna on Syria's conflict are expected to include discussion of which members of the fragmented opposition will attend any final negotiations on a peace deal.

Here are some of the main groups operating inside Syria and abroad:

As yet another round of talks gets underway on Syria in Vienna on Saturday, here is a recap of efforts to end the four-year-old conflict:

- ARAB INITIATIVES -

A U.S. strike on Syria that targeted British militant "Jihadi John" was "an act of self defense", Britain's Prime Minister David Cameron said Friday while acknowledging his death was "not yet certain".

Cameron said the operation against Mohammed Emwazi, who appears in a string of graphic videos showing the execution of Western hostages, was a combined British-U.S. effort.

Syria's army, backed by allied forces and Russian air strikes, seized a key rebel town south of Aleppo on Thursday, scoring its second major advance in the province this week.

State television announced the capture of al-Hader, a former opposition bastion near the key Aleppo-Damascus highway, just 48 hours after regime forces broke a siege by the Islamic State group of the Kweyris air base in the east of Aleppo province.

Turkish President Recep Tayyip Erdogan on Wednesday called on world leaders to rally behind Turkey's plan for a safe zone inside Syrian territory, days before it hosts the G20 summit.

Speaking to a group of businessmen in the capital Ankara, Erdogan said the Syrian conflict would be a "major topic" at the G20 summit in the Mediterranean resort of Antalya on Sunday and Monday.

The U.N. peace envoy for Syria urged world powers Tuesday to build on the "momentum" of new international talks and come up with a political process to end the four-year war.

"The momentum in Vienna needs to not be missed," Staffan de Mistura told reporters after briefing the U.N. Security Council.

U.S. and Russian military officials talk twice daily about air operations in Syria, as the two powers conduct separate bombing campaigns in the battered nation, a top U.S. general said Tuesday.

Four-star Air Force General Herbert Carlisle outlined how communications have vastly improved since the start of Russia's bombing campaign in Syria on September 30.

Air strikes by Gulf Arab members of the U.S.-led coalition fighting the Islamic State group in Syria have diminished since they launched an air war against Yemeni rebels in March, a U.S. general said Tuesday.

Bahrain, Saudi Arabia and the United Arab Emirates have carried out air strikes against IS in Syria but the three Gulf Cooperation Council members are also involved in an air and ground campaign in Yemen in support of exiled President Abedrabbo Mansour Hadi.

Russia's Foreign Minister Sergei Lavrov on Monday said countries will hold "enlarged" talks on the Syrian conflict soon, accusing some of trying to evade negotiations.

Speaking in the capital of Armenia at a press-conference, Lavrov said the list of players attempting to find common ground over the conflict that killed 250,000 people has grown since last month's unprecedented talks in Vienna.

The next meeting in Vienna on the Syrian conflict must draw up a list of "terrorist groups", Iranian Foreign Minister Mohammad Javad Zarif said on Monday.

"There are two important items on the agenda for the next meeting of Vienna," Zarif told a news conference with his visiting Belgian counterpart Didier Reynders.