Singapore said on Monday it has detained an assistant child-care worker suspected of trying to join Islamic State and to find a militant husband in Syria, and was holding her under a tough security law that allows for detention without trial.

The detention of the first Singaporean woman for suspected Islamist radicalism comes as concern is growing about the spread of Islamic State in the region. Singapore and its neighbours recently began intelligence cooperation aimed at stemming the movement of militants across their borders.

Singapore has reiterated over the past year that it is a target of Islamist groups and has urged the public to be alert.

The suspect, Syaikhah Izzah Zahrah Al Ansari, 22, was detained this month for intending to make her way to Syria to join Islamic State of Iraq and Syria with her child, the Ministry of Home Affairs said in a statement.

"She supported ISIS's use of violence to establish and defend its self-declared 'caliphate', and aspired to live in it," the ministry said, referring to Islamic State.

Izzah, a contract assistant at an infant care centre, was radicalised as early as 2013 by online propaganda with links to Islamic State and she shared pro-Islamic State material on social media.

She had also sought a militant husband in Syria, the ministry said.

"She said that since 2015, she was looking for 'a Salafi or an ISIS supporter' to marry and settle down with him and her child in Syria," the ministry said.

"She said she would support her husband if he fought for ISIS in Syria as she believed she would reap ‘heavenly rewards’ if he died in battle. With her ‘elevated status’ as a ‘martyr’s widow’, she felt she could easily marry another ISIS fighter in Syria."

Izzah has been detained under the Internal Security Act, a colonial-era law that allows authorities to detain anyone seen as a threat to security for up to two years.

Three male Singaporeans have been detained under the act over the past year.

Two of them were "Syria-bound militants" while the third was detained for "terrorism-related activities" which included supporting Islamic State and encouraging violence through Facebook posts.

Diverse, affluent Singapore is majority ethnic Chinese with sizeable minority ethnic Malay and ethnic Indian communities, and numerous foreign workers from Asia and beyond.

Singapore said late last year it had deported nearly 70 foreigners including five maids for suspected radicalism over the previous two years.

Authorities in neighbouring Indonesia, which has the world's largest Muslim population, said last year they had arrested six Indonesian suspects with links to Islamic State who were plotting an attack on Singapore.