Russia, US, Saudi, Turkey to hold Syria talks Thursday: Russian source

Top diplomats from Russia, the United States, Saudi Arabia and Turkey will hold a second round of Syria talks in less than a week in Vienna on Thursday, a Russian diplomatic source said on Wednesday.

Following the four-way meeting at 1800 GMT on Thursday the quartet could be joined for more talks on Friday by their counterparts from Iran, Egypt, Iraq and Lebanon "if these countries reply positively" to an invitation from Washington, the source said. 

The US said on Tuesday that a "genuine multilateral invitation" was made to Iran, a key ally of Syrian President Bashar al-Assad, to join the talks, despite earlier opposition from Washington and Riyadh. 

Iran announced on Wednesday that its foreign minister will attend the talks.

"We have reviewed the invitation, and it was decided that the foreign minister would attend," foreign ministry spokeswoman Marzieh Afkham said, without disclosing when Javad Zarif would arrive.

Friday's talks in Vienna are seen as a way to end Syria's civil war by creating an interim unity government and paving the way for Assad's exit.

A meeting last Friday in the Austrian capital between the top envoys from the four countries ended without a major breakthrough, as serious divisions remain over when or if Assad should go.

Russia launched air strikes in Syria last month to help forces loyal to Assad battle what it says are Islamic State and other "terrorist" groups.

The US and its allies involved in a bombing campaign against the Islamic State group insist Moscow is mainly targeting moderate groups fighting Damascus.