THE Indonesian police raised the alert on its border on Thursday after Singapore said a militant group leader had escaped and possibly headed to Indonesian territories, especially through small islands in Riau.

'Singapore has contacted us and they want us to take measures to prevent the suspect, Mas Selamet Kastari, from escaping to Indonesia,' Riau Islands provincial police chief Brig Gen Sutarman was quoted by the national Antara news agency as saying.

Sutarman said Singapore police had asked for close coordination with Riau Islands police to recapture the fugitive. 'They have also sent out a red notice,' he said.

'He knows well how to enter Indonesia,' said Sutarman.

The JI militant was arrested in Indonesia for immigration offences several years ago and then deported to Singapore who sought him for a plot to blow up the Changi Airport and hijack a Singapore plane.

Separately, National Police spokesman Sisno Adiwinoto said it was less likely that Mas Selamat would hide in Indonesia, where he has been jailed twice and local people were familiar with his face, Xinhua news agency reported on Thursday.

'He is possibly still somewhere in Singapore, or already in Malaysia by now,' Sisno told Jakarta-based Metro TV.

The Indonesian Police will remain cooperative with their Singapore's counterpart as it did when first deported Slamet.

'This is a terrorism case, we must be vigilant,' he said.

'And we hope that Singapore will be cooperative too in capturing Indonesian criminals and sending them back to Indonesia, primarily those convicted of economic crimes,' he said.

Mas Selamat bin Kastari, the alleged leader of al Qaeda-linked Islamic militant network Jemaah Islamiah's (JI) Singapore cell, escaped on Wednesday from the toilet of a detention centre.

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

The escape led to an apology from the government over the 'security lapse', and a manhunt involving thousands of policemen.

Experts said they believed Mas Selamat would try to return to Indonesia, where security is generally viewed as not as tight compared with Singapore.

'I believe he will try to get into Indonesia where he could avoid being detained a lot easier than in Singapore,' said Clive Williams, a professor at Australia's Macquarie University, who lectures on terrorism.

The city-state, which has a population of 4.6 million, has a wide network of surveillance cameras in public areas and security breaches are rare.

Wong Kan Seng, Singapore's minister for home affairs, acknowledged the lapse should never have happened and said everything was being done to arrest Mas Selamat.

'The priority is to arrest him, no effort will be spared to track him down,' Mr Wong told members of the parliament.