UN and Arab League envoy Lakhdar Brahimi has met internal opposition groups in Syria.
AAP reports Mr Brahimi held talks on Tuesday at a hotel in Damascus with a delegation of six led by Hassan Abdel Azim, head of the National Co-ordination Committee for Democratic Change, an opposition group tolerated by the regime.
Azim said afterwards that Brahimi would stay in Syria until Sunday "to try to implement an international consensus to end the crisis".
NCCDC deputy Raja Nasser said: "The only solution is a transitional government that holds all powers.
"A political solution is the only solution, and this means the establishment of a new democratic regime instead of the current regime."
Le Figaro newspaper in France earlier reported a US-Russian proposal that would involve keeping President Bashar al-Assad in power until 2014, while preventing him from further renewing his mandate.
But the Muslim Brotherhood has dismissed any compromise that would leave Assad in power.
"We consider that giving Assad the opportunity to commit an endless string of crimes is tantamount to complicity in these crimes," it said.