Speaking in his weekly radio address on Saturday, Obama said the US air force would continue to strike the Islamist militant group that has dubbed itself the "Islamic State" (IS) "if necessary."

He reiterated a pledge to protect American citizens serving in Iraq, and said the US would continue to do what it could do to help thousands of members of Iraq's Yazidi religious minority, who have become trapped atop Sinjar mountain without food or water after having fled from advancing IS militants into the city of Sinjar a week ago.

"The thousands - perhaps tens of thousands - of Iraqi men, women and children who fled to that mountain were starving and dying of thirst. The food and water we airdropped will help them survive," Obama said. "I've also approved targeted American airstrikes to help Iraqi forces break the siege and rescue these families.

The US air force launched its first airstrikes against IS forces on Friday, after Obama announced that he had authorized them. Friday also saw the US air force begin the airdrops of food and water that Obama referred to.

Though he stressed that as US commander-in-chief he would not order American ground forces to return to Iraq to fight IS militants, he also expressed the determination not to allow them to achieve their goal of creating a caliphate state on Iraqi and Syrian territory.

"We'll help prevent these terrorists from having a permanent safe haven from which to attack America," Obama said.

IS militants advance

IS fighters have claimed a large chunk of Iraqi territory in recent weeks, most notably the country's second-most populous city, Mosul. Over the past week, IS started moving north, toward Iraq's partially autonomous Kurdish territory, which borders Turkey.

In total, the United Nations estimates that more than half a million people have been displaced by the IS advance, many of them fleeing into Iraq's northern-most Dahuk province, in Kurdish territory.

In the western German city of Bielefeld, meanwhile, organizers aid they hoped that a major demonstration of the country's Yazidi population would draw a turnout of around 10,000 people on Saturday.

pfd/mkg (AFP, dpa, Reuters)