Rights groups have condemned the crackdown

There has been mounting international concern at the campaign, which has left more than 1,000 people dead since it started on 1 February.

Human rights groups have accused the authorities of encouraging extra-judicial killings, but Thai officials assured foreign diplomats on Monday that the campaign was being carried out under the rule of law.

Thai authorities have claimed that most deaths are the result of inter-gang warfare.

Don't be moved by the high death figures, we must be adamant and finish this war Thai Prime Minister Thaksin Shinawatra

Foreign ministry spokesman Sihasak Pheungketkaew said he had told diplomats on Monday that every death would be investigated.

He said that 50 police officers were are already being investigated, and that they would be "subject to prosecution as anyone would be" if they were found to have operated outside the law.

Police have acknowledged that their officers were responsible for 31 of the deaths, all of which were shot in self-defence.

However, Thai Prime Minister Thaksin Shinawatra did concede on Saturday that some of the deaths may not have been legitimate.

"It's normal that we have some mistakes in such a big war and a few cases may be work of officers since there are some bad officers," he said.

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

The prime minister said that two committees made up of lawyers and senior police officers, which were set up last week, would look into allegations of police misconduct.

He also said that about 700 government employees would be investigated for their alleged role in the drugs trade, and that the campaign, which is targeting the country's booming methamphetamine trade, could carry on beyond the initial three-month plan.

"Don't be moved by the high death figures, we must be adamant and finish this war," he urged.

Thailand is the world's largest consumer of methamphetamines - a powerful stimulant also known as speed or uppers.