London, Sep 26 (IANS): British Prime Minister David Cameron Friday said that the Islamic State (IS) was a threat to the "streets of Britain" and it was the "duty" of the government to confront the Sunni radical group, media reports said.

Cameron in his address to parliament, which debated Britian's involvement in the US-led attacks on IS positions in Iraq, said there was a strong case for Britain joining in the airstrikes against the militant group, BBC reported, adding that the prime minister also warned members of parliament that the fight would "take years not months".

"...We should be in no doubt that future British prime ministers and future British governments, I suspect, will be standing at this despatch box, dealing with this issue of Islamist extremism in different forms and in different parts of the world for many years to come," he said.

Joining airstrikes against the IS would be "clearly lawful", Cameron said. "I don't believe there is a legal barrier because I think the legal advice is clear that - were we to act or others to act - there is a legal basis."

He said Britain wanted to support its "Muslim 'friends' reclaim" their religion.

"We are dealing here with a generational struggle caused by the perversion of one of the world's great religions, Islam," the Guardian quoted him as saying.

"We will play our part in destroying these evil extremists, we will support our Muslim friends around the world as they reclaim their religion... our inspirational armed forces will put themselves in harm's way to keep our people and our country safe."

The British parliament is due to vote on the country's involvement in the US-led attacks on IS positions in Iraq at about 5 p.m.

The Conservatives, Liberal Democrats and Labour all back the action, which the coalition says is legal because it was requested by the Iraqi government.

The IS has seized large parts of Iraq and Syria in recent months. The group has used tactics that have included beheadings of soldiers, Western journalists and aid workers.