A teenager was sentenced to 12 years in prison today for joining a group of militants that was plotting terrorist attacks in Malaysia, a deputy public prosecutor said.

The 17-year-old man was among five people arrested while making homemade bombs outside Kuala Lumpur in April last year, deputy public prosecutor Raja Zaizul Faridah Zaharudin said.

The High Court in Kuala Lumpur found the teenager guilty of promoting acts of violence and imposed the long sentence to send a message that terrorism cannot be taken lightly, Raja Zaizul added.

The other four who were arrested, all adult males, were sentenced to between 20 and 25 years imprisonment earlier in the month.

The suspects plotted to bomb government buildings and entertainment centres in the capital and outlying areas, Raja Zaizul said.

Authorities have made strong efforts to curb the spread of militant ideologies in predominantly Islamic Malaysia, detaining nearly 200 people since they began a crackdown on local militants in early 2013.

Police estimate that nearly 100 Malaysians have gone to Syria and Iraq to fight alongside Islamic State militants.

Malaysian security forces have been on alert since January after bombings in Indonesia's capital Jakarta that killed several people.

Last week, 14 suspected supporters of the Islamic State, including an aircraft engineer, were arrested in police counter-terrorism raids in Kuala Lumpur and in the states of Selangor, Johor, Kedah, Perak and Perlis.

- dpa