LONDON - British police said Wednesday they foiled a suspected plot to murder King Abdullah of Saudi Arabia when he made a state visit here last year.

Detective Superintendent Mark Holmes, head of the National Terrorist Financial Investigation Unit, said they disrupted the plot, which they believe was being masterminded by Saudi dissidents.

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"We seized $330,000 (220,000 euros) in a cash disruption exercise at (London's main) Heathrow airport," he told a counter-terrorism conference of Britain's most senior police officers in Brighton, on England's south coast.

"The money was coming to the United Kingdom for distribution around UK-based Saudi dissidents. We suspect this was going to be used to facilitate the murder of Crown Prince (King) Abdullah."

The money, found on a courier stopped at the airport after a tip-off from an informant, was made up of 100-dollar bills. But detectives said there was insufficient evidence to bring charges against the cash smuggler.

Holmes, whose unit includes officers from British intelligence and the government's revenue and customs department, said the case showed how money was an essential resource for any active extremist network.

King Abdullah visited Britain as part of a European tour last October -- the first Saudi monarch to do so for two decades -- and met Prime Minister Gordon Brown and Queen Elizabeth II.

But his visit, although high on pomp and ceremony, was also controversial and he faced protests from human rights activists and anti-arms trade campaigners.

Opponents said Britain was turning a blind eye to human rights abuses in the oil-rich Gulf state in order to secure lucrative defense contracts and co-operation countering extremism.

Saudi Arabia has previously accused Libya of being behind a plot to assassinate King Abdullah in 2003, when he was crown prince.

He pardoned the five Libyan intelligence agents accused of the plot who were detained in Saudi when he became monarch after the death of his half-brother king Fahd.