LONDON — Nearly 100 people have been arrested for illegally selling tickets and bogus hotel rooms ahead of the London Olympics, a top British security official said Wednesday.

With some six months to go before Britain's largest-ever planned security operation, Home Secretary Theresa May said police had already arrested 97 people for touting tickets, setting up fake websites and selling phoney hotel rooms.

Demand for tickets and hotels in London is huge -- some rooms are going for more than 600 pounds per night (nearly $1,000).

"Police are sending a very clear message that we're not going to tolerate intrusions by organized criminals into the Olympic Games," May said during a speech at the Royal United Services Institute in London, a British security think-tank.

But the threat most on the minds of organizers is terrorism -- Britain was the first western European country targeted by al-Qaida-inspired suicide bombers who launched simultaneous attacks in 2005 on London's transit system, killing 52 people the day after London won its Olympics bid.

Intelligence officials say there's nothing to suggest a specific and credible terror threat to the games, yet the government threat level will rise to "severe."

Britain's police, the domestic spy agency MI5, the foreign intelligence agency MI6, government communications surveillance units and the military will all help secure the Olympics against possible threats. In addition, international law enforcement and policing agencies like Interpol and the FBI will also help British authorities. More than 20,000 security guards are also being hired to add extra protection.

"Many resources will be dedicated to counterterrorism operations," said Commander Bob Broadhurst, in charge of operational planning for Scotland Yard. He said one concern is being able to patrol events around the Olympics, such as concerts and other celebrations.

Although Broadhurst said protests would be allowed during the games, May said protest camps around key sites would be prohibited.