The public execution by firing squad of five convicts in Thailand has provoked strong criticism from human rights groups.

Four of those executed were major drug smugglers, reflecting the hardline approach to an escalating drug problem by the new government of Prime Minister Thaksin Shinawatra.

The fifth man had been convicted for masterminding a murder.

"It is outrageous for the new Thaksin government to flaunt its tough anti-drugs stance by executing people," London-based Amnesty International said.

"The death penalty provides no solution to growing crime rates... Instead it entrenches a culture of violence in society."

Thailand's Union for Civil Liberty also condemned the executions.

'Crazy drug' problem

The executions come amid fears that the government is losing the battle against the rising drug problem, said to affect two million people out of the Thailand's population of 60 million.

Synthetic methamphetamine (speed) pills, made across the border in Burma, have flooded the country in recent years.

The police estimate that this year, 800 million of the highly-addictive tablets will enter Thailand - enough to give 12 pills to every person in the country.

"Ya Ba" or "crazy drug", has been described as the number one national security issue, particularly affecting the young.

In 1999, there were more than 660,000 cases of drug-related offences by students.

Thaksin firm

Amnesty said it recognised the "gravity of the illicit drug problem in Thailand" but added there was no evidence that the death penalty was a more effective deterrent.

But Prime Minister Thaksin has stood firm, saying the men had destroyed the future of a large number of young Thai people and deserved to die.

The authorities say they intend to speed up the execution of people condemned for drug offences.

The five men were executed on Wednesday by machine gunfire in Bangkwang Prison. Three were Thais, one Taiwanese and one a citizen of Hong Kong.

One man, Vichien Saenmahayak, 42, was found with 50,000 methamphetamine pills while another, Boonkerd Jitpranee, 40, was found with over 30kg of heroin.