The United States says it has carried out four new airstrikes on Islamist extremists in northern Iraq.

The U.S. military says the latest action was undertaken to defend Yazidi refugees fleeing the Islamist militants and taking refuge on Mount Sinjar in northern Iraq.

Aid drops are also continuing, with aircraft from the US and UK bringing supplies to the civilians trapped in the mountains. The civilians fled when the Islamic State (formerly known as ISIS/ISIL) threatened them with death.

The Pentagon is targeting Islamic State fighters and the latest attacks hit armoured vehicles and other targets. President Barack Obama has said Washington will provide military assistance to Baghdad and Kurdish forces but has insisted Iraq must work to solve the problems itself and must work towards forming an inclusive government. Much of the support for the Islamic State has come from Sunni Muslims in Iraq who have felt persecuted and marginalised by the Shia government of Nouri al-Maliki.

The militants are now just half an hour from Arbil, the Iraqi Kurdish capital. The Kurdish area of northern Iraq was the one success story of post-2003 Iraq, with the violence and sectarian battles of southern Iraq never taking root in the region.