The Western- and Arab-backed Syrian Free Army (FSA) has sacked its leader and replaced him with a more experienced field commander as part of a revamp of moderate forces fighting President Bashar al-Assad, opposition sources said on Monday.

A statement by the FSA's Supreme Military Council said it replaced General Selim Idriss, who had served in the Corps of Engineers of Assad's army, with Colonel Abdelilah al-Bashir, head of FSA operations in the province of Qunaitera on the border with the Israeli-occupied Golan Heights.

The decision was prompted by "the ineffectiveness of the command in the past few months... and to provide leadership for military operations against the criminal regime and its allies from terrorist organizations," said the statement.

The announcement was made on Sunday after a Supreme Military Council meeting in Turkey attended by Asaad Mustafa, defense minister in a provisional government set up by the opposition last year, the sources said.

Dissident rebels have long been wary of accepting leadership by Idriss, who has spent most of his time outside Syria since helping create the Supreme Military Council in December 2012.

During his tenure, the FSA suffered major setbacks.

Loyalist forces backed by Shi'ite fighters from Iran, Iraq and Hezbollah regained strategic territory in the province of Homs in the centre of the country and expanded a buffer zone around Damascus, where most elite troops, mostly comprised of Assad's minority Alawite sect, are based.

Al-Qaeda-linked groups also emerged as a potent force on the ground, and several Islamist brigades broke off from the FSA, helping create the Islamic Rebel Front, which overshadowed the FSA militarily.

A statement by the opposition National Coalition, which has embarked on U.S.-and Russian-sponsored peace talks with Assad's government to end the three-year civil war, said news of Bashir's appointment came as a "relief".

The coalition's delegation added several FSA commanders to its negotiating team in the second round of peace talks, which concluded on the weekend in Geneva without any significant results.