Neither of the groups, however, have much influence over the disparate armed factions fighting to overthrow President Bashar Assad. The Syria-based opposition ranges from officials close to the government, to intellectuals and parties that have opposed Assad's Baath party for decades. The exiled group ranges from secular intellectuals to Islamic activists.
In its statement Monday, however, the exiled Coalition said it would only attend the Geneva talks if humanitarian aid is allowed to reach besieged areas and the government releases political prisoners. The group itself wants any future transitional government to exclude Assad and his close allies a demand the Syrian government has rejected.
The proposed Geneva conference faces a series of obstacles: the most powerful and best-armed rebel groups aren't party to the talks, and most fighting units are disorganized bands with little central command or leadership. Even if an agreement is reached in Geneva, it is unclear if it will be accepted on the ground.
As the fighting continues, troops loyal to Assad were on the march. In their latest blow to rebel fighters, government forces took the town of Tel Aran and a series of other positions in the northern province of Aleppo, state media said, a day after they consolidated their control of a key military base held by rebels since February. The British-Based Syrian Observatory for Human Rights, which receives its information from a network of activists on the ground, backed the state media's reports.
The Observatory and an Aleppo activist said they believed the government's gains were partly caused by rebel infighting. The al-Qaida-linked Islamic State in Iraq and the Levant in particular, they said, was trying to drive weaker rebel groups from rebel-held areas.
On Monday, for example, ISIL fighters attacked another rebel group on a mountainous hillside in the coastal province of Latakia, the Observatory and the activist said.
"We are afraid of ISIL more than the regime," said the activist, who requested anonymity for fear of retribution.
"The ISIL is not fighting the regime. It is seeking to expand, it is trying to seize the liberated areas and announce its Islamic rule," he said, adding that infighting had grown steadily over the past three months.
Also Monday, Syria's state news agency said a mortar shell hit a school bus in the Bab Sharqi neighborhood of central Damascus, killing four children and the bus driver. It said four children and two teachers were also wounded.
The Observatory also reported a death toll of five people in the attack.
Mortar shells also hit a Greek Orthodox church in Damascus and wounded around a dozen students at a nearby school.
With reporting by Albert Aji in Damascus and Desmond Butler in Istanbul.