Describing Singapore's execution rate as "shockingly high" and "shrouded in secrecy", Amnesty called on the government to impose a moratorium on all executions and immediately commute all death sentences to prison terms.

About 400 people have been hanged in Singapore since 1991, mostly for drug trafficking, giving the wealthy city-state of four million people possibly the highest execution rate in the world relative to population, Amnesty said.

Singapore's drug laws are among the world's harshest. Anyone aged 18 or over, convicted of carrying more than 15 grams of heroin faces mandatory execution by hanging. 

But there was "no convinving evidence" this had curbed drug use, Amnesty said, citing Singapore Central Narcotics Bureau statistics, showing 3393 people arrested for drug offences in 2002 and the number of new drug abusers up 16 % from 2001. 

"We are also calling on the authorities to end the secrecy about the use of the death penalty and encourage public debate"

Amnesty International

"We are also calling on the authorities to end the secrecy about the use of the death penalty and encourage public debate," the human rights group said in an 18-page report titled Singapore: The Death Penalty - A hidden toll of Executions. 

Between 1994 and 1999, an average of 13.57 executions were carried out for every one million of the population, three times higher than the next country on the list, Saudia Arabia, it said. 

The Prisons Department said 400 executions since 1991 was a "fair estimation". 

The government does not normally publish statistics about death sentences, or give the number of prisoners on death row.