US President Barack Obama on Tuesday was to urge lawmakers to endow him with new war powers to defeat Islamic State militants, warning the battle would be long but eventually successful.

"This effort will take time. It will require focus. But we will succeed," Obama was to say, according to excerpts of his State of the Union address released by the White House.

"In Iraq and Syria, American leadership -- including our military power -- is stopping ISIL's advance," the commander-in-chief was to tell US lawmakers.

"Instead of getting dragged into another ground war in the Middle East, we are leading a broad coalition, including Arab nations, to degrade and ultimately destroy this terrorist group," Obama was to say.

"We're also supporting a moderate opposition in Syria that can help us in this effort, and assisting people everywhere who stand up to the bankrupt ideology of violent extremism."

But in order to emerge victorious, Obama will appeal to gathered lawmakers to give him a new authorization to use military force against the Islamic State group, also known as ISIL, which has seized a swathe of territory in Iraq and Syria.

The US has already unleashed dozens of airstrikes against the militants since September, using the powers enshrined in legislation adopted in the wake of the September 2001 attacks to hunt down Al-Qaeda and its affiliates.

But US officials have argued that a new Authorization for Use of Military Force is needed.

"Tonight, I call on this Congress to show the world that we are united in this mission by passing a resolution to authorize the use of force against ISIL," Obama was to say. (AFP)