The rebel Free Syrian Army (FSA) said Sunday it had fired Selim Idriss as its military chief, citing the "difficulties faced by the Syrian revolution" in its battle with the regime, AFP reports.
In a video broadcast on the Internet, the rebel coalition said its military council had decided to replace Idriss with Brigadier General Abdel al-Ilah al-Bachir.
Colonel Qassem Saadeddine said the decision was taken due to "the paralysis within the military command these past months" and the need to "restructure".
A source inside the Syrian opposition told AFP that Idriss - who was appointed to the role in December 2012 - had faced criticism for failings on the battlefield.
These included "errors and carelessness in combat" and "poor distribution of weapons" among the rebels on the ground, the source told the news agency.
He is also accused of distancing himself from "the concerns of the insurgents."
The group's new leader Al-Bachir is the head of the military council in the southern province of Quneitra. He deserted the regular army in 2012.
According to the FSA Facebook page, Al-Bachir's son was killed in fighting at the beginning of the year.
Considered the "moderate" rebel group, the Western-backed FSA was once the country's strongest armed opposition force but is now increasingly marginalized by Islamists.
It has been weakened by internal rifts and by competition from other rebel coalitions such as the Islamic Front, a powerful alliance formed last year that is now the largest rebel force with tens of thousands of fighters.
The FSA has also been attacked by its jihadist rivals who, after splitting off from the “moderate” opposition, declared Aleppo to be an independent Islamist state and have summarily executed members of the Western-backed rebel groups.
In December the United States and Britain suspended non-lethal aid to the FSA, dealing a major blow to a group that appears caught between advancing regime forces and the increasingly unified Islamists.
The move came after the Islamic Front - which has said it wants to set up an Islamic state in Syria - seized weapons warehouses from the FSA.
The FSA's decision to replace Idriss comes after peace talks between the Syrian regime and the opposition in Geneva ended without reaching any results, throwing the future of the negotiations to end the bloody conflict into doubt.
On Saturday, Syria's regime accused Israel and the United States for undermining the UN-brokered peace talks and blamed the opposition's refusal to settle the issue of "terrorism" for the deadlock.