Six civilians were killed and 13 injured Monday when Iraqi helicopters fired at areas near the town of Biji, the site of a major oil refinery.

>Iraqi forces were chasing fighters of the Islamic State of Iraq and the Levant (ISIL) when the helicopters fired upon some houses in the town, located some 200 km north of Baghdad. Insurgents had reportedly been hiding in the buildings.

Last week, the government said its forces had taken full control of the country’s largest oil refinery, after days of clashes with Islamist-led insurgents.

Earlier this month, ISIL, an al-Qaeda splinter group, seized the northern Iraqi city of Mosul and made a swift advance to capture a string of towns stretching south towards Baghdad.

Biji is around 50 km away from Tikrit, another major battleground between Iraqi forces and the radical Sunni rebels.

ISIL on Sunday declared an Islamist caliphate in Iraq and Syria, in an audio clip on Twitter. Spokesman Abu Mohammed al-Adnani said in the recording that ISIL leader Abu Bakr al-Baghdadi is the first caliph of the self-described state and that all Muslims are obliged to swear their allegiance to him.

The authenticity of the recording was not immediately confirmed.

The insurgents’ swift advances have raised international fears that Iraq is disintegrating and that the fighting could allow a regional militant enclave to emerge.

Iraq has suffered increasing violence during the last year, much of it blamed on ISIL and aimed at security forces and Shiite civilians.

The government’s response, with security sweeps and mass arrests, has further alienated Iraq’s Sunni minority, from which ISIL and other rebel groups draw their support.