The UN is said to be worried by the scale of the killings

Pradit Charoenthaitawee said on Friday that he was "desperate" over the threats, which also targeted his family.

"They said they had put a bomb under my car, send amphetamines to my house, or burn my house down," Mr Pradit said.

The human rights group Amnesty International has called on the Thai Government to protect Mr Pradit, and launch an immediate investigation.

Drug war figures More than 1,000 dead Police say 31 shot in self-defence 46,177 on interior ministry blacklist 29,501 arrests, according to police 700 government officials under investigation

In a UN speech in Pakistan last month, Mr Pradit highlighted his concerns over the drugs crackdown, which has left more than 1,000 people dead in its first month.

The government blames the high number of deaths on inter-gang violence, but human rights activists say that there is a "shoot to kill" policy in operation.

The Thai Government has also threatened Mr Pradit with impeachment if he continued to criticise government policy openly.

Suranand Vejjajiva, the ruling party spokesman, told the BBC's East Asia Today programme on Thursday that Mr Pradit should be careful.

"If he starts accusing the Prime Minister of being a dictatorship... that that there is state-sponsored violence, that's not right," Mr Vejjajiva said.

Prime Minister Thaksin Shinawatra has also said Thais should not act at "whistleblowers" or "give away Thailand's independence".

Government role

Mr Vejjajiva denied that the government was responsible for the killings.

"The government did not sponsor any killings. We do not condone any killings, but we have to be firm in the war on drugs," he said.

But Giles Ungkhaporn, a human rights activist, told East Asia Today that he was outraged by the government's actions.

"The government has shown absolutely no regard for human rights. It's certainly not true that the government is not responsible for the deaths. It is responsible," he said.

"It is the Prime Minister, the Minister of the Interior and the Chief of Police who should be going through the impeachment process," he added.

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.