The US military says it has carried out four new air strikes on militants to defend civilians in northern Iraq.

US Central Command said jet fighters and drones had destroyed armoured carriers and a truck that were firing on members of the Yazidi sect.

Thousands of civilians fled into the mountains after the Islamic State (IS) overran the town of Sinjar a week ago.

This is the third round of US air strikes since they were authorised by President Barack Obama.

The previous strikes targeted IS (formerly known as Isis) forces threatening the Kurdish city of Irbil.

A US military statement said the latest strikes had been defending members of the Yazidi religious group who were being “indiscriminately attacked” near Sinjar.

It said a mix of fighter jets and drones destroyed an IS armoured personnel carrier (APC) that was firing on civilians.

The statement said US aircraft then monitored movement of other APCs and an armed truck and attacked them.

The series of strikes is the first time US forces have been directly involved in a military operation in Iraq since they withdrew from the country in late 2011.

The Pentagon also said a third US air-drop of food and water had been made on Saturday night to refugees on Mt Sinjar.