President Barack Obama has said he has full authority to press on with military action in Iraq against Isis (now known as the Islamic State) and does not need Congress approval to do so.

However, Obama sought support from Congressional leaders to show that the US is in unison while dealing with the crisis.

The White House said in a statement that Obama "reiterated his belief that the nation is stronger and our efforts more effective when the President and Congress work together to combat a national security threat".

"The president told the [Congressional] Leaders that he has the authority he needs to take action against ISIL in accordance with the mission he will lay out in his address tomorrow night."

Obama met leaders from both parties ahead of the formal announcement of Washington's game plan which is set to take place on Wednesday evening.

House Speaker John Boehner and Senate minority leader Mitch McConnell – both Republicans -- and Democrats Harry Reid, Senate majority leader, and Nancy Pelosi, House minority leader, were present at the meeting.

Following the meeting, Boehner said in a statement that he would back Obama if the US forces are mobilised in Iraq to train and advise the Iraqi personnel.

The Congress had earlier stonewalled Obama's efforts for military action in Syria last year aimed at uprooting the Damascus regime led by President Bashar al-Assad.

The Obama administration has constantly ruled out deploying ground troops in Iraq and Syria against Isis, despite harsh criticism from conservatives and others by calling it a timid response. However, the president has signalled his intention to widen military action.

The latest development in Washington is taking place as Secretary of State John Kerry is in the Middle East coordinating US efforts to garner assistance from other nations against Isis.