Cameron urges parliament to back Iraq action

Prime Minister David Cameron addresses the Houses of Parliament on Friday during the debate on military action against Islamic State. 

AFP/London

British Prime Minister David Cameron warned on Friday that military action against Islamic State (IS) militants could last for "years" as he urged lawmakers to back joining US-led air strikes in Iraq but not in Syria.

Kicking off a crunch debate in the House of Commons, Cameron said the "hallmarks" of the campaign would be "patience and persistence, not shock and awe".

"This is going to be a mission that will take not just months but years but I believe we have to be prepared for that commitment," he said, between a barrage of questions from lawmakers about the length and scope of the mission.

The debate has awakened memories in Britain of its role in the deeply unpopular US-led invasion of Iraq in 2003 under then prime minister Tony Blair.

But Cameron argued that the situation then was entirely different and the government has emphasised that lawmakers will not vote on sending combat troops.

"This is not 2003 but we must not use past mistakes as an excuse for indifference or inaction," he added.

Six British Tornado fighter jets based in Cyprus are poised to begin raids on IS within days or even hours if the vote, due at 5pm, is passed.

Britain would join the US and France in launching targeted strikes on the IS group in Iraq, where it controls swathes of territory, as in neighbouring Syria.

IS fighters have beheaded a British aid worker, David Haines and two US journalists, and are holding two other Britons, Alan Henning and John Cantlie.

Britain does not propose, as yet, joining US-led air strikes on Syria, which are backed by five Arab states. Cameron said a separate parliamentary vote would be needed for that to happen.

He admitted there was "no consensus" on action in Syria, although he said that "Britain should do more" there.

Some lawmakers, for whom the 2003 invasion remains a painful memory, are expected to oppose military action because of fears that the mission is ill-defined.