Singapore has the highest execution rate in the world relative to its population, outstripping China, Saudi Arabia and Sierra Leone, Amnesty International said in a report released Thursday.

More than 400 prisoners have been hanged since 1991 in the Southeast Asian city-state of 4 million people, the London-based rights organization said in a report on Singapore entitled “A Hidden Toll of Executions.”

“It is the cold-blooded killing of a human being by the state in the name of justice, and violates one of the most fundamental of all human rights: the right to life,” Amnesty said in a statement, describing the number of executions in Singapore as “shockingly high.”

Most executions were for drug offenses while some were for murder and firearms offenses, all of which carry mandatory death sentences in Singapore, the report said.

Those executed overwhelmingly came from disadvantaged groups: migrant workers, drug addicts, the poor or the uneducated, Amnesty said. It cited the case of Rozman Jusoh, a 24-year-old Malaysian laborer who was hanged for drug trafficking in 1996, despite having below normal intelligence with a reported IQ of 74.

The government says it needs the death penalty to deter drug addiction and violent crime.

“By protecting Singaporeans from drugs, we are protecting their human rights,” said Inderjit Singh, a member of parliament, responding to the report.

“The rule breakers have to be dealt with — it’s the same in any part of the world,” said Singh, who is also president of a chip-making company. “We just do it differently.”

Singapore drug laws are among the world’s toughest. Anyone caught with more than half an ounce of heroin or more than 17 ounces of marijuana is presumed to be trafficking and faces a mandatory death sentence.

Singapore had the highest per capita execution rate between 1994 and 1999, with about 13.6 executions for every million people, according to the latest U.N. report on capital punishment.

That figure is more than six times the rate for China, which had the largest overall number of executions. Singapore’s rate was nearly three times that of Saudi Arabia and more than four times that of Sierra Leone.

Since 1991, there have been about 747 executions in the United States, a nation of about 290 million people, according to Richard Dieter, the executive director of the Washington-based Death Penalty Information Center.

Amnesty charged that Singapore denied defendants the right to be presumed innocent until proven guilty by writing laws ordering that they be presumed guilty of trafficking based on the amount of drugs found.

The group also accused the government of veiling its use of the death penalty by failing to regularly publish statistics about death sentences or executions. The number of prisoners currently on Singapore’s death row is not known, it added.

Only the rare occasions when the government responds to a parliamentary question on the issue provide glimpses into the tally of executions, the report said.

However, the government says the process leading to executions is public.

“All trials involving capital cases are tried in an open court,” home affairs ministry spokesman Goh Kiat Teng said. “All judicial decisions involving the death penalty are open to public scrutiny.”