Barack Obama has announced an expansion of America's military action in Iraq and Syria, in a bid to "degrade, and ultimately destroy" Islamic State extremists.

The US President says he's increasing airstrikes in the region and has promised resources to equip and train Iraqi forces but in his address, he stopped short of sending in American forces to take on the militants.

"We will hunt down terrorists who threaten our country, wherever they are," Mr Obama said. "That means I will not hesitate to take action against ISIL (IS) in Syria, as well as Iraq.

"This is a core principle of my presidency: If you threaten America, you will find no safe haven."

In the last few weeks, IS has released videos of its militants beheading kidnapped American journalists James Foley and Steven Sotloff.

Mr Obama announced that he was sending around 500 more US troops to Iraq to assist its security forces and urged Congress to authorise a programme to train and arm Syrian rebels who are fighting both the Islamic State militants and President Bashar Assad.

However, he insisted it "will not involve American combat troops fighting on foreign soil".

"This counter-terrorism campaign will be waged through a steady, relentless effort to take out ISIL wherever they exist using our air power and our support for partner forces on the ground.

"This strategy of taking out terrorists who threaten us, while supporting partners on the front lines, is one that we have successfully pursued in Yemen and Somalia for years."