Islamist militants have taken control of the Iraqi city of Tikrit as Nouri Al-Maliki’s central government continues to lose its grip on security in northern Iraq.

Tikrit, which lies 150 kilometres north of Baghdad, represents the second major city claimed by Islamic State of Iraq and the Levant (Isis) after insurgents seized Mosul on 10 June.

On 11 June there were also reports of fighting in Kirkuk province – the centre of Iraq’s oil assets in northern Iraq – and the city of Samarra, 110km north of Baghdad.

The Isis attacks have been condemned by the UN and the US government, which said it would support a response by Baghdad to launch a counterattack against the insurgents.

According to reports, Iraqi security forces offered little resistance in Mosul and Tikrit to the Isis fighters, who took over police stations and, in Mosul, released hundreds of prisoners.

Al-Maliki has vowed to fight back against Isis forces and asked parliament to declare a state of emergency, which would expand the government’s powers to make arrests and enforce curfews.

Isis, which grew out of an Al-Qaeda-linked organisation in Iraq, is estimated to have up to 5,000 fighters holding a territory stretching from the eastern side of Aleppo in Syria to Fallujah – less than 100 kilometres west of Baghdad.