The regime of Bashar al-Assad was yesterday hit by its most serious defection so far as activists said Syria’s recently appointed prime minister had joined the revolution and state media announced his sacking.

The whereabouts of Riyad Hijab remained a mystery. But his defection came amid further signs of intensifying instability in Syria.

Although the Syrian prime minister and his government are not part of the inner Assad circle, the defection of Mr Hijab – a Sunni member of the ruling Ba’ath party – underlines the accelerating erosion of support for the minority Alawite regime fighting a 17-month revolt by the majority Sunni population. It also highlights the gradual collapse of the Syrian state, which relies heavily on Sunni bureaucrats and officials.