SINGAPORE'S government has come under stinging public criticism after the escape of an alleged militant leader from custody dented the country's reputation for airtight security.

Letters to the editor and Internet blogs by Singaporeans took officials to task for the escape on Wednesday of Mas Selamat bin Kastari, alleged leader of the Singapore wing of the militant Islamic group Jemaah Islamiyah.

Open criticism of the government is rare in tightly ruled Singapore, but the apparent ease with which Kastari managed to slip out of a detention centre raised questions about the authorities' anti-terrorist measures.

Kastari was accused of plotting to hijack a plane in order to crash it into Singapore's busy Changi Airport in 2001, but never charged in court. He was being held under an internal security law which allows for detention without trial.

The Ministry of Home Affairs said Kastari escaped after he was permitted to use the toilet during a visit by family members.

'I am sure Singaporeans would like to know the details of the escape - what happened from the time the terrorist left for the restroom while his family members were waiting for him,' said a letter from reader Rosemary Chwee published on Saturday by Singapore's leading daily, The Straits Times.

'Such a slip is professionally unforgivable... As a citizen, I am deeply concerned, especially if Mas Selamat continues to be on the loose,' she wrote.

Police flyers seeking public help in recapturing the 47-year-old Kastari say he is 'not known to be armed' and walks with a limp.

'What puzzles me is how a middle-aged man who has difficulty walking can leave the detention centre with such ease,' wrote another reader, Siow Jia Rui.

Another letter writer, Lee Beng Hai, suspected Kastari could have been helped by 'sleepers and sympathisers'.

Internet blog sites - the usual refuge of Singapore government critics who are denied space in the mainstream media - were full of chatter and conspiracy theories on the escape.

Even the Straits Times, which is closely identified with the government, said in an editorial that the authorities had to confront the question of whether Kastari had help.

'It stretches credulity to imagine this was an opportunistic solo effort... The escape was too easy, too neat,' it said.

If he had help, it would mean 'terror cells are still morphing and sympathisers are being drawn into the network', the newspaper said.

If he acted alone, 'the system breakdown was egregious', it added.

'Security incidents like this one... will shake confidence in the anti-terror system.'

The editorial said complacency may have set in because Singapore has been spared from terrorist violence so far.

Since the September 11, 2001 attacks in the United States, Singapore has implemented tough security measures and rounded up suspected militants and sympathisers of the Jemaah Islamiyah.

The group has been blamed for a series of attacks including the 2002 bombings on the Indonesian resort island of Bali which killed 202 people, mostly tourists.

Kastari, a Singaporean citizen of Indonesian ancestry, was handed over by Indonesian officials after his second arrest there in 2006.

Singapore is a predominantly ethnic Chinese city-state which has a Malay Muslim minority and hosts hundreds of thousands of foreign workers, many of them Malaysians and Indonesians. -- AFP