'Strategy on Islamic State includes support for Syrian oppn, Iraq'

US President Barack Obama on Wednesday will announce his plan to defeat Islamic State militants in Iraq and Syria in a speech to Americans that the White House said will discuss direct US military action as well as support for forces fighting the group in both countries.

The White House, in a statement ahead of the speech, said the United States "will pursue a comprehensive strategy to degrade and ultimately destroy" the Islamic organisation. The speech will be carefully watched for indications of how much Obama is prepared to intervene directly into Syria, riven by civil war and whose leader Washington has sought to dislodge.

Obama is schedule to speak at 9 pm EDT (0100 GMT Thursday).

He also will discuss his administration's effort to build international support for the US plan among allies and others in the region and work with Congress, the statement said.

The White House has said Obama has the authority he needs to take action against the Sunni Muslim group, which is seeking to establish an Islamic state and has taken over huge swathes of land in Iraq and Syria. US officials have said there is no imminent threat of attack against the United States but the group has beheaded two US captives in the region in recent weeks.

So far, the United States has carried out limited airstrikes in parts of Iraq aimed at destabilising the organisation and Obama has ruled out sending in US combat forces.

Obama could order airstrikes on an expanded list of targets within Iraq and has been considering strikes in Syria as well, on condition that moderate rebels there be in a position to hold territory cleared of Islamic State fighters by the strikes.

Obama came close to direct military action a year ago in Syria to support what Washington considers more moderate rebel forces fighting President Bashar al-Assad, but held off given strong opposition in Congress. After disgust in America over the videotaped beheading of two American journalists by Islamic State in the past month, resistance in Congress has diminished.

But Washington's failure since then to support the moderate groups has left them weakened and it is unclear how the United States can build up such forces quickly enough to create a useful military ally on the ground.

Obama has shown a willingness to intrude militarily into Syrian space with an unsuccessful operation in July to try to rescue Americans held hostage by Islamic State, and he said in an interview that aired on Sunday that Washington was prepared to hit the group's leaders wherever it could.

Iraq's formation of a relatively inclusive government on Monday has cleared the way for wider U.S. action in support of Iraqi armed forces and Kurdish forces in a country where the United States was engaged in a bitter military struggle for nine years after overthrowing President Saddam Hussein. Secretary of State John Kerry arrived in Baghdad on Wednesday to meet with Iraqi leaders and discuss efforts to combat Islamic State.

Polls this week show the majority of Americans support action against the militants.

More than 70 percent of Americans support airstrikes in Iraq and 65 percent support using them in Syria, a Washington Post-ABC News opinion poll found. An NBC News-Wall Street Journal poll showed 61 percent said military action against the group was in the interest of the United States.

Still, Obama, who was elected in 2008 on a promise to get U.S. troops out of Iraq and did so by the end of 2011, must make his case to the public and build support from Congress.

Obama met with key lawmakers on Tuesday and administration officials are expected to give wider briefings on Thursday. U.S. lawmakers have been mixed on whether Congress must authorize any wider U.S. military action in the region.

Representative Mike Rogers, the Republican head of the House Intelligence Committee, told CNN that Obama's speech was critical and called it "a good start" to combating a serious threat, saying the president needs to leave room for other possible action, such as sending in special U.S. forces.

Senator Angus King, a Maine independent and member of the Senate intelligence and armed service committees, cautioned it will be impossible to oust the militants with air power alone.

"There are going to be boots on the ground. The only question is whether they're American or Iraqi or Kurdish," he told CNN. "The real question we have to face is: is the safe haven argument sufficient to justify significant American engagement."