Islamist militants and Iraqi forces are engaged in fierce battle for control of the Baiji oil refinery and Tal Afar airport in northern Iraq.

Rebels from the Islamic State of Iraq and al-Sham (ISIS) claim to have seized most of the Tal Afar airport and have surrounded and moving in on the Baiji refinery.

The battles come after the US President Barack Obama ruled out sending US troops to fight the insurgents on the ground, but did commit to sending 300 military advisers to help fight the insurgents.

The US has not ruled out air strikes, but does not want to become embroiled in a sectarian conflict or be seen to be propping up Iraq Prime Minister Nouri Maliki, who has been accused of pursuing anti-Sunni policies and alienating the 20% of the population that follows the Sunni Islam tradition.

Sunni grievances against the government have been exploited by ISIS, who subscribe to an extremist version of Sunni Islam, and helped the group gain a foothold in Iraq.

ISIS has moved quickly through northern Iraq since the group seized control of the city of Mosul on 11 June, after a number of Iaqi military units fled the area after coming under fire.

Oil fields and refineries have been central to the growth of ISIS, with the group becoming the richest terrorist organisation in the world with around $2bn in the bank, on the back such seizures in Syria during the ongoing conflict.