A member of Al-Jabha Al-Islamiya (the Islamic Front) takes position on a armored vehicle at a checkpoint in Idlib on Jan. 6, 2014.

A powerful alliance of Syrian Islamist rebels on Sunday rejected peace talks that begin this week, meaning that even if the talks reach an unlikely breakthrough in the three-year-old civil war, it will be harder to implement any agreement on the ground.

Syria's main political opposition group in exile, the Syrian National Coalition (SNC), agreed on Saturday to attend the talks that will begin in Geneva on Wednesday. This seemed to set up the first meeting between President Bashar al-Assad's government and groups in rebellion.

But the Islamic Front, an alliance of several fighting forces that represents a large portion of the rebels on the ground, said it rejects the talks.

Syria's future would be "formulated here on the ground of heroism, and signed with blood on the front lines, not in hollow conferences attended by those who don't even represent themselves," said Abu Omar, a leading member of the Islamic Front, on his Twitter account.

The decision by the Islamic front comes as the SNC leadership is in Istanbul to decide on its delegation for the opening of Wednesday's peace talks.

Senior Coalition member Ahmad Ramadan said the meeting will decide who will negotiate with the Syrian government delegation at the so-called Geneva 2 conference.

The conference aims to broker a political settlement to the conflict based on a roadmap adopted in June 2012 by the United States, Russia and other major powers. That plan includes the creation of a transitional government with full executive powers.