A 'SECURITY LAPSE' led to the escape of the leader of the Singapore's wing of the Islamic militant network, Jemaah Islamiah (JI), and drew an apology from Home Affairs Minister Wong Kan Seng on Thursday.

Mr Wong Kan Seng, who is the Deputy Prime Minister, told Parliament that Mas Selamat Kastari, who walks with a limp, escaped from the toilet of the Whitley Road Detention Centre, near a wooded park on Wednesday afternoon.

Acknowledging that the security lapse 'should have never happened', Mr Wong said all stops are being pulled out to capture the JI militant, who was linked to a sensational plot to crash a hijacked plane onto Changi Airport.

He is still on the run more than 24 hours after he fled on Wednesday at about 4.05 pm, as a massive manhunt involving thousands of police, military and special operation command forces continue to track him down.

The JI has been blamed for several deadly bombing attacks in Southeast Asia, including the 2002 bombings that killed more than 200 people on Indonesia's resort island of Bali.

Mas Selamat left Singapore after plots to attack Changi Airport and other targets, including the US embassy, the American Club and the Singapore American School, were foiled seven years ago.

Nearly 40 other suspected members of JI were rounded up.

He was arrested by the Indonesian police on the Indonesian island of Bintan in January 2006 and sent back to Singapore.

He had since been held under Singapore's Internal Security Act, which allows for detention without trial.

Giving an update on how the JI leader escaped on Wednesday afternoon, Mr Wong said he was being led to a room to meet his family members who were visiting him when he asked to go to the toilet.

Mr Wong apologised for the 'security lapse at the Whitley Detention Centre'.

'This should never have happened. I am sorry that it had. An independent investigation is underway and we should not speculate on what and how it happened,' he said, adding that security at the centre had since been stepped up.

Mr Wong added: 'He is a security threat which is why he was placed under preventive detention, However, there is no information that he has any plans that threaten public security. Nevertheless, we are not taking any chances.'

On why the public was informed of the escape only four hours after the escape, Mr Wong said the escape posed no 'imminent danger to the public' at the time.

'The focus then was to lock down the Whitley Road detention centre and then to start a systemic operation to find and arrest him. The priority is to arrest him and no effort will be spared to track him down,' he said.

Elaborating, he added that the security at all the air, land and sea checkpoints have been tightened, including 'the areas where he may leave our shores not from the normal immigration clearance areas'.

He also warned that anyone who helps Mat Selamat would be committing a serious offence. 'I urge the public to stay calm and report any suspicious sightings to the police immediately,' he said.