Britain and the US have warned they will rethink support for Syria's main opposition group if it fails to join peace talks, a Syrian source has said.
The official from the Syrian National Coalition told reporters that the UK and the US were adamant the group must go to Geneva for next week's talks.
The coalition will hold a vote on Friday on whether or not to attend.
Syria's opposition remains deeply divided nearly three years after the uprising began.
It is hoped that the talks in Switzerland - known as Geneva II - will provide a breakthrough in ending the bitter civil war.