Iraqi government forces have begun an offensive to retake the city of Ramadi from the jihadist group Islamic State (IS), officials say, teh BBC reports.

A spokesman for the Counter-Terrorism Service, Sabah al-Numani, said troops and militiamen, backed by the air force, had entered the city centre.

They were advancing towards the main government complex, he added.

Ramadi, about 90km  west of Baghdad, fell to IS in May in an embarrassing defeat for the Iraqi army.