The White House revealed to lawmakers on Tuesday details of its request to Congress for a three-year war authority to battle Islamic extremists that would prohibit "enduring" offensive combat operations.

The authorization for use of military force (AUMF) would also allow for use of US special forces, and would not restrict operations to a geographic area, several Democratic senators said after a closed-door briefing by White House officials.

President Barack Obama's team has been deliberating for months on how to move ahead in the next phase of its years-long war against militant jihadists.

The White House is expected this week to unveil its proposal for authority to combat the Islamic State extremist group, and administration officials have stepped up their deliberations with congressional leaders.

The new AUMF would supersede the open-ended war authority which Congress passed in the aftermath of the 9/11 attacks in 2001. The administration currently uses the 2001 authority to prosecute military action against IS, in particular US-led air strikes on the group's forces in Iraq and Syria.

Lawmakers have stressed that no official war authority language has been released.

"It was an opening salvo," Senate Democratic leader Harry Reid said after the briefing. "There was nothing finalized yet."

Democratic Senator Robert Menendez said a key plank of the proposal, according to the White House briefers, required "no enduring offensive combat" operations, a qualifier he acknowledged could face opposition in Congress.

"Unless that is further defined, that might be seen as too big a statement to ultimately embrace because, forget about Barack Obama, there would be a new president in two years," Menendez said.

"The challenge to get a broad bipartisan AUMF is threading the needle between not having too expansive an authorization that can be used for an open-ended, prolonged conflict, and however giving an authorization that gives the president the wherewithal to effectively defeat ISIL."

Senator Dianne Feinstein said she understood that the request for a three-year authorization would allow for special operations.

But "I think the big discussion will be over how you word the language on troops," the top Democrat on the Senate Intelligence Committee said.

Some Republicans were already pushing back.

"I will agree to nothing that restricts the president's latitude of action," hawkish Senator John McCain told reporters.

Language barring enduring combat operations "would be unacceptable to me," he said, adding that any debate about the war authority should not be rushed.

Republican Senator Lindsey Graham said he was briefed by the White House by phone and was disturbed that the new authority would not allow US forces to protect US-trained Syrian rebels against air attacks by strongman Bashar al-Assad's military.

"I'll be a no to that," he said.

'Imminent' terror attack foiled in Australia: police
Sydney (AFP) Feb 10, 2015 - Australian police Wednesday said an "imminent" terror attack has been foiled in Sydney with two men arrested and a machete, a hunting knife, a video, and an Islamic State flag seized.

New South Wales Deputy Police Commissioner Catherine Burn said it would be alleged that the attack being planned was "consistent with the messaging coming out of IS".

Asked whether the planned attack was a beheading, Burn said police were as yet unsure of its nature but that it was imminent and likely to have involved a knife.

"We believe that the men were potentially going to harm somebody, maybe even kill somebody, and potentially using one of the items that we identified and recovered yesterday, potentially a knife," she said.

The men were arrested in a raid on a property in Sydney's western suburbs on Tuesday and have been charged with undertaking acts in preparation or planning for a terrorist act.

"A number of items were located including a machete, a hunting knife, a home-made flag representing the prescribed terrorist organisation IS, and also a video which depicted a man talking about carrying out an attack," said Burn.

"We will allege that both of these men were preparing to do this act yesterday. We built up information, we received further information which indicated an attack was imminent. And we acted."

Australia in September raised its terror threat level, and carried out extensive raids in Sydney and Brisbane to disrupt an alleged plot by IS supporters to abduct and behead a member of the public.

The Islamic State group is a brutal jihadist organisation that has captured swathes of territory across Iraq and Syria and sucked in increasing numbers of radicalised Australians to its cause.

In December, Sydney was rocked by a siege at cafe by Iranian-born Man Haron Monis, a self-styled cleric with a history of extremist views.

He took 17 people hostage for some 16 hours, with the siege ending after Monis shot dead cafe manager Tori Johnson, prompting police to storm the building and kill him. Another hostage died in the crossfire.

Prime Minister Tony Abbott on Monday reiterated that the cafe siege was inspired by the Islamic State "death cult".

Burn said she did not know the exact nature of the target in this week's alleged attack but that one of those arrested featured in the video seized.

"We can't go into the details of what was actually said in that message," she said. "However, the intent is clear and the intent is what I have told you today."