Mr Thaksin is now travelling in an armoured van

Mr Thaksin told reporters that drug kingpins had put a bounty on his head in retaliation for a war on drugs which has killed more than 1,000 people since it began on 1 February.

"Reports have come from our intelligence units that a group of international mafia bosses want to kill me," Mr Thaksin said. "This is not a mere threat, they are real," he added.

Mr Thaksin's administration has been accused by human rights groups of pursuing a shoot to kill policy against perceived drug dealers. Bangkok says that most of those who died were the victims of inter-gang fighting, and 31 were shot by police in self-defence.

If someone calls and threatens me, I feel nothing... Dogs who bark don't bite Thai Prime Minister Thaksin Shinawatra

Mr Thaksin said his personal security had been tightened. He said he now travelled in an armoured van rather than his usual sedan, and that sniffer dogs were scouring Government House.

He refused to confirm the price on his head, but Thai media quoted security sources on Wednesday as saying that drug kingpins living along the Thai-Burmese border had offered a bounty of 80m baht ($1.89m) to assassinate Mr Thaksin.

An official from the Office of Narcotics Control Bureau (ONCB) told the French news agency AFP that drug lords from Burma's ethnic Wa group, who are blamed for producing most of the methamphetamines that flood Thailand, could be responsible.

"We believe the Wa are behind the reward because they are the group which has been affected most from our war on drugs campaign," he told the agency.

But Mr Thaksin said he was not afraid.

Drug war figures 1,498 dead, according to police Police say 31 shot in self-defence 46,177 on interior ministry blacklist At least 700 government officials under investigation

"If someone calls and threatens me, I feel nothing... Dogs who bark don't bite. The dog who bites will not bark," the prime minister said.

The boosted security follows the fatal shooting at the weekend of an aide to Interior Minister Wan Muhamad Nor Matha, who is overseeing Thailand's drugs war.

Thailand is the world's largest consumer of methamphetamines - a powerful and addictive stimulant known locally as "ya-ba".

About 5% of the population regularly abuse the drug, according to the International Narcotics Control Board.