The group previously known as the Islamic State in Iraq and the Levant has renamed itself “Islamic State” and has established a caliphate over territory it has captured in both Syria and Iraq.

Its leader Abu Bakr al-Baghdadi has been declared the “caliph for Muslims everywhere” in a statement posted on Twitter and several Islamic websites.

Meanwhile, the Iraqi Ministry of Defence has released footage reportedly showing troops advancing on the northern city of Tikrit with the aim of regaining control with an assault backed by tanks and helicopters

Security officials said the army is coordinating its campaign, which was launched on Saturday, with the United States.

If the Tikrit operation is successful it could help to restore a degree of faith in the Iraqi security forces and be a boost to Prime Minister Nouri al-Maliki’s government.