Iranian-backed militias have sent reinforcements from Iraq into Syria to bolster Bashar al-Assad’s regime against a lightning advance by rebel groups.

Tehran said it would provide full support to the beleaguered dictator after the insurgents seized the city of Aleppo and then charged south toward Hama.

Government troops were on Monday reported to be building a fortified defensive line in northern Hama in an attempt to stall the offensive, which has reignited the Syrian civil war after years of stagnant front lines.

An Iraqi militia official said Tehran-backed forces already in Syria had mobilised and additional troops had crossed the border to support Assad’s government and army.