"This should never have happened. I am sorry that it had," he said, adding that security at the centre had since been stepped up.
"An independent investigation is under way and we should not speculate on what and how it happened."
Wong said Mas Selamat was being taken to see his visiting family when he asked to use the washroom and made his escape.
Asked why the public was informed only four hours after the escape, Wong said the escape posed no "imminent danger to the public" at the time.
Believed to have received military training in Afghanistan and joined JI in early 1990s, taking over its Singapore arm in 1999
Accused of planning to attack buildings in Singapore such as defence ministry and US embassy
Also accused of plotting to hijack a jet in Bangkok and crash it into Singapore's Changi airport in revenge for associates' arrest
Arrested by Indonesian authorities for having false identification papers
Held under Singapore's Internal Security Act without trial since March 2006
Military personnel were mobilised on Thursday to reinforce police who had set up roadblocks and combed the area throughout the night.
The alert also went out to all border checkpoints, the coast guard, and even taxi companies, urging cab drivers to look out for the suspect.
The Internal Security Department's Whitley detention centre is located in a quiet, wooded area just a few kilometres from Singapore's main shopping district.
Homes and several schools are within walking distance and the centre has no watch-towers, unlike other prisons in Singapore.
Several schools near the detention centre were searched and ringed by police as classes continued, but many parents took their children out of school for the day, Singapore's Straits Times daily reported.
Singapore, a close ally of the US, was named an al-Qaeda target during alleged al-Qaeda operative Khalid Sheikh Mohammed's tribunal at Guantanamo Bay, Cuba, last year.
The Singapore government says the Indonesian-born Mas Selamat plotted to crash an aircraft into the country's airport and was involved in plans to attack Singapore government buildings and the US embassy there.
|Mas Selamat allegedly asked to go to |
the washroom before escaping [Reuters]
He avoided a 2001 dragnet in Singapore that netted 13 JI suspects. Indonesian authorities detained him in February 2006 for carrying false identification papers and handed him to Singapore in March.
Singapore has held him since under its Internal Security Act, which allows indefinite detention without trial.
Another 27 people are being detained under that law for alleged involvement in terrorist activities.
Another 31, most of them former JI members, have been released from detention but remain on Restriction Orders which limit their activities.