Assad regime forces and Syrian opposition were locked in talks Wednesday night to reach a 15-day ceasefire in the Eastern Ghouta region east of the capital, a monitor and a security source told AFP.These are the first known talks aiming for a truce in the region and are likely being brokered by Russian or Iranian mediators, the Syrian Observatory for Human Rights said.If agreement is reached, "a ceasefire in Eastern Ghouta would begin at 6:00 am (0400 GMT) Thursday and will last 15 days," Observatory head Rami Abdel Rahman said.A senior Syrian security source told AFP "talks are ongoing between the government and a number of armed groups in Eastern Ghouta... to stop military operations," without giving further details."Our Russian allies are playing a direct role in contacting those that support the armed groups," he said.Jaish al-Islam, the most powerful rebel group in Eastern Ghouta, was the main negotiating partner on the rebel side, Abdel Rahman added.A spokesman for the group could not be reached for comment.An AFP journalist living nearby said fierce shelling could still be heard in Eastern Ghouta, which is the largest rebel stronghold near Damascus and is regularly bombarded by regime forces. The talks come days after top diplomats from 17 countries met in Vienna to seek an end to Syria's conflict, which has left more than 250,000 people dead since it erupted in 2011.US Secretary of State John Kerry said Tuesday Syria could be weeks away from a "big transition."Rebels and regime have reached local ceasefires near Damascus in the past, but Eastern Ghouta would be the most significant yet. In September, warring parties reached a six-month truce in Zabadani, the last rebel stronghold on Syria's border with Lebanon, as well as two Shiite Muslim villages in northwest Syria.Brokered by the United Nations, the agreement included aid deliveries and evacuations for civilians and wounded fighters.