US President Obama says he 'has authority' to widen IS fight
President Barack Obama has said that he has the authority to widen military action against Islamic State (IS) militants in Iraq and Syria without the approval of Congress.
He will still ask Congress to approve the arming of Syrian opposition forces.
Mr Obama is due to give a speech on Wednesday night in which he will outline his anti-IS strategy.
IS militants have taken over large parts of Syria and Iraq in recent months and have declared a "caliphate".
In the past month, IS militants have beheaded two US journalists in protest against American airstrikes on its forces in Iraq.
Mr Obama's moves come as Secretary of State John Kerry goes to the Middle East in an effort to build up regional support for a coalition to combat IS.
Mr Kerry is travelling to Jordan and Saudi Arabia for talks with officials from 10 Arab states and Turkey.
Meanwhile the Saudi ambassador in London, Prince Mohammed bin Nawaf, rejected suggestions that his government was supporting or funding IS.
"It is the lack of international involvement that has paved the way for terrorist-affiliated movements to breed within Syria, and now Iraq," he said in a statement.
"We have previously urged the international community to take an in-depth look at the financial backing and organisational structure of this terrorist organisation.
"Had this been carried out it would have been revealed that rather than being the instigator of such terrorist network Saudi Arabia is in fact the main target."
'No ground operation'
Mr Obama discussed his anti-IS strategy with leaders from both parties at the White House on Tuesday. A spokesman said the talks were "productive".
The meeting with Congressional leaders came a year after lawmakers blocked Mr Obama's previous plans for missile strikes against Syria.
Mr Obama has ruled out the possibility of a US ground operation against IS but has signalled he may expand airstrikes to include Syria.
"Over the course of months, we are going to be able to not just blunt the momentum of [IS]," he said on Sunday. "We are going to systematically degrade their capabilities; we're going to shrink the territory that they control; and, ultimately, we're going to defeat them."
At the White House on Tuesday, he met Democrats Senate Majority Leader Harry Reid and House Minority Leader Nancy Pelosi, and Republicans John Boehner, the speaker of the House of Representatives, and Mitch McConnell, the Senate minority leader.
The White House said Mr Obama had told the congressional leaders he welcomed action from Congress in support of the effort and pledged "continuing extensive consultation".
But Mr Obama's aides suggested he would not seek new authorisation from Congress for military action.
"The president told the leaders that he has the authority he needs to take action against [IS] in accordance with the mission he will lay out in his address tomorrow night," the White House said.
Mr Obama will make a televised speech from the White House at 21:00 local time on Wednesday (01:00 GMT Thursday).
Mr Boehner, one of Mr Obama's chief political adversaries, told the president he would back a US military deployment to train and advise the Iraqi security forces and assist in the targeting of IS leaders, an aide to the House speaker said in a statement to the BBC.
According to a new Washington Post-ABC News poll, a large majority of the American public views Islamic State as a serious threat to the US and widely supports air strikes in Iraq and Syria.
About 100 Americans are believed to have joined the militants and the US state department has tried to counter this by making a hard-hitting video that tries to dissuade potential recruits.
Meanwhile, France has announced it will host an international conference on Iraq on 15 September and President Francois Hollande will visit the country later this week.