British tourists to Thailand are being warned to take "extreme caution" at a popular island resort following reports of an increased threat from terrorists.

The Foreign Office says it has intelligence reports that suggest the threat to British nationals visiting Phuket has "increased significantly".

The warning comes following the bomb attack on a nightclub in Bali that killed more than 190 people, mainly foreign tourists, including up to 30 Britons.

A Foreign Office spokeswoman said: "The advice is kept under constant review. The changes that we made reflect the latest information made available to us.

"We have now included the popular tourist area of Phuket."

The Foreign Office website warns British institutions and businesses to reconsider their security arrangements, adding that British and international schools should be "especially vigilant".

Denmark and Australia have already warned their nationals to be on their guard when visiting Thailand.

Phuket, off the country's west coast, draws many thousands of foreign tourists every year to its ocean-side resorts.

The island is particularly popular with backpackers.

Following the Bali bombing, the Foreign Office came under pressure to reveal whether it had had any warnings of an imminent attack on the Indonesian island resort.

Cleric quizzed

Foreign Secretary Jack Straw later revealed no specific warning had been received.

Meanwhile, Indonesian police have released sketches of three men they suspect of involvement in the Bali attack.

Indonesian police are also questioning Abu Bakar Ba'asyir, an elderly cleric, about a series of attacks in South-East Asia over the last two years.

The cleric is also the alleged leader of the militant Muslim group Jemaah Islamiah, which authorities suspect of involvement in the Bali bombing.

Australia and the United States are helping Indonesia with the investigation into the blast.