LONDON - Prime Minister David Cameron, grappling with what could prove a defining crisis of his premiership, told parliament on Thursday that rioters behind Britain's worst violence in decades would be tracked down and punished.

"The fightback has well and truly begun," he said in a statement to an emergency session of parliament, telling rioters: "You will pay for what you have done."

Cameron is under pressure to soften austerity plans, toughen policing and do more for inner-city communities, even as economic malaise grips a nation whose social and perhaps racial tensions have exploded in four nights of bewildering mayhem.

The British leader said he would keep a higher police presence of 16,000 officers on London streets through the weekend and would consider calling in troops for secondary roles in future unrest to free up frontline police. Among other measures, he said he would give police powers to demand the removal of face masks or other coverings if their wearers were suspected of crime, and pledged to crack down on criminal "street gangs" to "help mend our broken society".

He also promised compensation for people whose homes or businesses were damaged by rioters, even if they were uninsured. Cameron had ordered a rare recall of parliament from its summer recess to debate the unrest which flared first in north London after police shot dead an Afro-Caribbean man. Britain's finance minister, George Osborne, will also address parliament amid concerns that the rioting could damage confidence in the economy and in London, one of the world's biggest financial centers and venue for next year's Olympics.

With the public seething over the looting of anything from sweets to televisions, Cameron has dismissed the rioters as no more than opportunistic criminals and denied the unrest was linked to planned spending cuts, mostly not yet implemented.

But community leaders say inequality, cuts to public services and youth unemployment also fed into the violence in London, Birmingham, Manchester and other multi-ethnic cities.

Reuters