SINGAPORE - Singapore Prime Minister Lee Hsien Loong said Friday the death of terror leader Noordin Mohammed Top in an Indonesian police raid was a 'significant achievement' that would make the region safer.

'This is a significant achievement that will make Indonesia and the region safer,' Lee said in a letter to Indonesian President Susilo Bambang Yudhoyono released by Singapore's foreign ministry.

But he also cautioned that while groups linked to Noordin would be weakened by his death, 'they still pose a threat to our countries and the region.'

Lee said Singapore would continue to work closely with Indonesia and other regional governments in the fight against militancy.

'I am confident that under your able leadership, and the professionalism of the Indonesian police and security agencies, Indonesia will score more successes against terrorists in future,' the Singapore leader said.

Noordin, a 41-year-old Malaysian who led a violent splinter faction of the Jemaah Islamiyah radical network, was killed along with three other militants during a raid on a village house in central Java on Thursday.

His death ended a six-year manhunt for the man blamed for a series of deadly suicide attacks including the July double bombing of Jakarta's JW Marriott and Ritz-Carlton hotels.

Singapore, one of Asia's most affluent cities and a regional base for thousands of multinational companies, is a prime target for attacks by militant groups, officials have said.

One of the plots foiled by Singapore authorities was a plan by Islamic militants to hijack an airliner in Bangkok and crash it into Changi airport in 2001 following the September 11 attacks in the United States.

Singapore has also arrested several militants allegedly involved in a plot to bomb the US embassy and other targets in the city-state.