The death of Zahran Alloush, 44, head of Jaysh al Islam, is a big blow to rebel control of the rural eastern suburban area of Damascus known as al Ghouta, the rebels said.

Defence experts say the disarray among the rebel forces could also consolidate Syrian President Bashar al-Assad's control over the rest of the area.

Several rebel leaders have been killed since Russia began an aerial campaign on Sept 30 in support of its ally Assad, although Moscow has insisted that it is concentrating its attacks on Islamic State.

The rebel sources said that in the raid Russian planes fired at least 10 missiles at a secret headquarters of the group, which is the largest rebel faction in the area and has about 15,000 to 20,000 fighters, according to Western intelligence.

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