The rebel Free Syrian Army has fired Salim Idriss as its military chief, calling him "ineffective" and lacking in experience to lead military operations on the ground.
In a video broadcast on the internet on Sunday, the rebel coalition said its military council had decided to replace Idriss with Brigadier General Abdel-ilah Albashir.
Colonel Qassem Saadeddine said the decision was taken due to "the paralysis within the military command these past months".
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A source inside the Syrian opposition told AFP news agency that Idriss, who was appointed to the role in December 2012, had faced criticism for failings on the battlefield.
Al Jazeera's Omar Al Saleh, reporting from Istanbul, said the Supreme Military Council said Idriss was "ineffective" and "lacked the military experience to run operations on the ground".
They also said he had bad relations with other rebel forces fighting on the ground.
"Combined with the failure of the Geneva talks, the head of the Syrian National Coalition returned to Syria and promised rebels in Idlib that they would soon be receiving more weapons and support," our correspondent said.
This restructuring is intended to raise morale amongst the FSA, once the country's strongest armed opposition force but now increasingly becoming marginalised by rival groups.
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.
In December, the US 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 Islamic Front.