Singapore has used its controversial 'fake news' legislation to try to suppress claims that death row prisoners are sometimes kicked to death to ensure their necks snap during botched hangings.

Key points: The claims come from a former hangman who worked at the Changi prison

The claims come from a former hangman who worked at the Changi prison Singapore denies the claims and has moved to censor them on social media

Singapore denies the claims and has moved to censor them on social media Human Rights Watch says Singapore is extremely secretive about how many executions it carries out

A former executioner at Singapore's Changi Prison has alleged that he and other prison officers were secretly ordered to kick the back of the neck repeatedly if a prisoner did not die from the gallows.

The man — who remains anonymous — recently told a Malaysian human rights group that prison officers were given special training to carry out the execution method.

"He and other prison officers were instructed to carry out the brutal procedure whenever the rope breaks during a hanging, which happens from time to time," the group Lawyers for Liberty (LFL) said in a statement.

The group said if a hanging fails to kill a prisoner on death row, officers are quietly instructed to work in pairs to break the person's neck.

"The officers are told not to kick more than two times, so that there will be no tell-tale marks in case there is an autopsy," Lawyers for Liberty said.

The statement also claims that the Singapore Government approved of these "unlawful" methods in "flagrant breach" of the country's constitution.

The Singaporean Government has rejected the allegations as "preposterous" and denied that it has ever used such a method to kill a death row prisoner.

"For the record, the rope used for judicial executions has never broken before. This fact alone shows the falsity of LFL's allegations," the government said.

"These scurrilous allegations of misconduct follow a series of sensational and untrue stories previously published by LFL."

Singapore demands group brand its allegations 'fake news'

The government has also invoked its 'fake news' law to demand the human rights group and others attach 'fake news' labels to their webpages or Facebook posts.

Singapore's Prime Minister Lee Hsien Loong introduced the 'Protection from Online Falsehoods and Manipulation Act' last year. ( Reuters: Feline Lim )

Singapore last year promoted its Protection from Online Falsehoods and Manipulation Act as a means to protect free speech and national security.

But opposition groups and rights activists have warned it will instead be used to silence criticism of the government.

"This is all about Singapore's effort to censor news that they don't like," said Phil Robertson from Human Rights Watch.

Lawyers for Liberty is standing by its statement and will refuse to attach a fake news label to its website.

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"Our statement is based upon evidence from former and current Singapore prison officers. These are officers with impeccable service records," the organisation said.

"This attempt by Singapore to extend their jurisdiction to Malaysian citizens … is provocative, illegal and in breach of international law."

The majority of executions in Singapore are for drug offences, including trafficking. ( Reuters: Nicky Loh )

Malaysians are believed to make up the majority of death row prisoners in Singapore, most of them convicted for drug trafficking.

Human Rights Watch says it is difficult to know who or how many prisoners in Singapore face the death penalty.

"Singapore is probably the least transparent country we deal with when it comes to the death penalty," Phil Robertson said.

"There is no listing of the number of people who are put to death, and who they were. There's nothing."

Human Rights Watch has asked for local observers to be given access to prisons to witnesses execution procedures.

"Singapore is doing none of it. So their denials have to come with a grain of salt," Mr Robertson said.

Human rights activists hold candlelit vigils outside Changi Prison in Singapore when executions are underway. ( Reuters: Nicky Loh )

Lawyers for Liberty has called for a moratorium on all executions in Singapore pending investigations into the allegations.

It has also demanded that Singapore reveal the number and identities of Malaysian prisoners who have been executed using kicking — instead of the proper gallows — in Changi.

In the wake of those statements, authorities in Singapore have ordered that the Lawyers for Liberty website be blocked.