Iraqi forces have launched an operation to retake areas of the Al-Anbar province, which was recently seized by the jihadist group Islamic State in Iraq and Syria (Isis).

Thousands of Iraqi security forces and Popular Mobilisation Forces – an umbrella organisation of Shia militia groups – have been gathering at the Habbaniya military base since Isis won control of Ramadi on 17 May.

Iraqi forces have surrounded Ramadi on three sides and there have been reports of ground fighting and air strikes west and south of the Al-Anbar capital.

The presence of Iran-backed Shia militias in the campaign has led to local concerns of growing sectarian divisions in the Sunni-majority province.

Ramadi is located 112 kilometres west of Baghdad and is the capital of Al-Anbar province, which is the country’s largest and covers the entire west of Iraq.

The fall of Ramadi has been viewed as a key turning point in the war against Isis, with commentators saying it is now impossible for Baghdad and Washington to claim that the Islamist militants are on the back foot in Iraq and Syria.

Both governments have accused each other of responsibility for the failure to hold on to Ramadi after Iraqi security forces fled the city under threat from a relatively small number of Isis fighters.

Al-Anbar has become the main front for Isis ground attacks in Iraq, along with the continued conflict at the country’s largest refinery at Baiji, north of Baghdad.

Isis is thought to have acquired heavy weaponry including tanks and missile launchers left behind by the government troops around Ramadi.