Obama to seek congressional approval for war against IS

President Barack Obama will send the US Congress a proposal to authorise the use of force against the Islamic State (IS) terrorist group shortly, both the White House and the House of Representatives Speaker John Boehner said, setting up what is sure to be a fierce political fight on Capitol Hill.

White House press secretary Josh Earnest said the administration would send "specific language" of an Authorisation for the Use of Military Force (AUMF) to Congress "relatively soon". Boehner said he was "expecting (an AUMF) sent up here in the coming days", CNN reported.

The president is required by law to secure congressional approval for prolonged military operations, by passing an AUMF -- war authority -- on Capitol Hill.

"When it comes to fighting a war, Congress should not tie the president's hands," Boehner said. "And we are going to go through a rigorous set of hearings and continue to discuss this."

The time line for the bill remains murky.

Obama went ahead with airstrikes in Iraq and Syria without Congress weighing in.

The president is required by law to ask Congress for war authority within 60 days of initiation, but the White House has argued that under the 2001 AUMF, which authorised war against the 9/11 perpetrators, he has the authority to attack IS because it's an offshoot of Al Qaeda.

But as far back as September and again in his State of the Union address this January, Obama urged Congress to pass the new authorisation.

"We are strongest as a nation when the president and the Congress work together," he said in September.

Boehner said the President is going to have to sell the measure both to Americans and on Capitol Hill, suggesting the responsibility for success or failure lies on his shoulders.

"It's also going to be incumbent upon the president to make the case to the American people for why we have to fight this fight," he said.

"His actions are going to be an important part of trying to get the votes to actually pass an authorisation... This is not going to be an easy vote."