Iraqi forces have withdrawn from the city of Ramadi despite assurances they would have the necessary air cover and militia reinforcements to hold their ground.

The effective loss of the capital of Iraq’s largest province of Anbar marked one of Baghdad’s worst setbacks since it began a nationwide offensive last year to reclaim territory lost to the jihadists in June 2014.

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ISIL said in an internet post it fully controlled Ramadi, after a local official admitted the operations command centre there had fallen.

“God has enabled the soldiers of the caliphate to cleanse all of Ramadi … after storming the 8th brigade. They (now) control it along with a battalion of tanks and missile launchers and in addition to the Anbar operations command,” the ISIL statement said.

Muhannad Haimour, spokesman and adviser to the provincial governor, said “Anbar operations command has been cleared”.

A colonel among troops who had withdrawn added: “Daesh (ISIL) has just taken full control of all main security bases.”

A spokesperson for Iraqi Prime Minister Haider al-Abadi said troops, tribesmen and elite forces “must hold their positions and preserve them and not allow Daesh to extend to other areas in Ramadi”.

“There is continuous air cover that will help ground troops there hold their positions while waiting for support from other forces and the Popular Mobilisation Units,” he said of an umbrella group for Shi’ite militias.

The International Organisation for Migration said two days of fighting in Ramadi had displaced around 8000 people.

Haimour said at least 500 people, both civilians and military, were killed in the jihadist offensive.

A local Anbar province official said Abadi had approved the dispatch of the Popular Mobilisation units known as Hashed al-Shaabi to Anbar.

“The provincial council of Anbar decided to call on Hashed al-Shaabi which operates under the umbrella of the commander in-chief of the armed forces,” Mahdi Saleh al-Numan, security adviser to the Anbar governor, said.

He said the forces would be drawn “from the disciplined brigades known for their honest work”, suggesting that some Shi’ite militias would not be called on.

The move marks a U-turn from the Sunni province’s previous opposition to resorting to the Shi’ite force.

The jihadists used a wave of suicide car bombings to take most of the city and raised their black flag over the provincial headquarters.

Taking full control of Ramadi, some 100 kilometres west of Baghdad, would be the most significant victory this year for ISIL, which has suffered a string of setbacks elsewhere in Iraq and Syria.