US President Barack Obama has told congressional leaders that he has the authority he needs to carry out a broader campaign against the Islamic State group, a day before outlining his plans to the American people in a prime-time address.

The White House on Tuesday said the president told lawmakers that he still would welcome action from Congress that "would aid the overall effort and demonstrate to the world that the United States is united in defeating the threat from ISIL".

That could take the form of congressional authorisation to fund counterterrorism efforts, as well as train and equip more moderate elements of the Syrian opposition.

The president's broader strategy to confront the Islamic State fighters may also include more wide-ranging airstrikes against targets in Iraq and possibly in Syria.

The US began launching limited air strikes against Islamic State targets in Iraq in August, action that occurred at the invitation of the Iraqi government but without specific authorisation from Congress.

Even before Obama's meeting with congressional leaders, some lawmakers had suggested a vote on the president's plans was unlikely before the midterm elections in November.

"As a practical matter, I don't really see the time that it would take to really get this out and have a full debate and discuss all the issues," said Republican Rep. Howard "Buck'' McKeon, chairman of the House Armed Services Committee.

Source: AP