Barack Obama insists anti-terror strategy is 'breaking the back' of Islamic State

He noted that he is poised to become the first president to serve two full terms at war, and defended a counter-terrorism strategy that has relied on US special forces and local groups rather than large-scale American ground forces.

The US has built a "network of partners" to help fight extremists and it is "breaking the back" of IS, he said.

His speech at the home of US Special Operations Command came as allies and foes alike await a potentially dramatic shift in American strategy towards addressing extremist threats overseas after Donald Trump takes office.

Before taking to the stage for his speech, Mr Obama told about 250 US service members gathered in a gym that it had been the privilege of his lifetime to serve as their commander-in-chief.

"I have been consistently in awe of your performance and the way you carried out your missions," Mr Obama said.

For the outgoing president, who came into office telling a war-weary nation he would wind down two wars and prevent new ones, the inclination towards smaller-scale, limited military involvement was a natural extension of his foreign policy philosophy. White House spokesman Josh Earnest said Mr Obama had believed that large troop presences in Iraq and Afghanistan were unsustainable.

"The strategy that President Obama has put in place is more effective, it keeps us safe, it has fewer American men and women in harm's way, and it costs American taxpayers a lot less," Mr Earnest said.

But Mr Obama's approach has most notably come up short in Syria, where he long ago predicted that US-backed forces would eventually prevail over Syrian president Bashar Assad. But Assad's grip on power appears stronger than it has in years while the brutal civil war continues to rage.

Mr Trump has said little about how he intends to shift course in Syria and whether he would continue Mr Obama's strategy in other regions destabilised by extremist groups. He has argued that ambiguity and unpredictability are assets that deny the enemy a chance to plan ahead.

Still, all signs suggest he will pursue a more muscular, military-driven approach to extremist groups like the Islamic State in Syria and Iraq.

Mr Trump has argued that Mr Obama's decision to withdraw the bulk of troops from Iraq, rather than negotiating harder with Baghdad to leave some there, created a power vacuum that allowed IS to form and seize territory.

During the presidential campaign, he said he would listen to top military officers about the need for ground troops to fight IS, at one point floating a figure of 20,000 to 30,000. Meanwhile, he has suggested that ousting Assad is not a top priority and that closer alignment between the US and Russia, which backs Assad, would be positive.

In the absence of more details from Mr Trump, attention has turned to the advisers he has selected to form his team, including retired General Michael T Flynn, tapped for national security adviser.

Gen Flynn, who has attracted controversy over his comments critical of Islam, has urged a far more aggressive military campaign against IS.

Mr Obama was promoting the benefits of his more limited approach on Tuesday.

Under his leadership, the number of US troops in Iraq and Afghanistan has dropped from roughly 180,000 to 15,000 today, according to deputy national security adviser Ben Rhodes.

Meanwhile, the US has been able to take out key al-Qaida leaders, most notably Obama bin Laden, and has started edging the Islamic State group out of strongholds like Mosul in Iraq and Raqqa in Syria.

AP