There are at least 50,000 Malaysians who are sympathisers of Islamic State (IS) militants, a senior official said today, warning that the threat of radicalism in the country cannot be ignored.

Transport Minister Liow Tiong Lai said the figure was based on police intelligence estimates.

"If only 1 percent of these sympathisers turn radical and if they attack any part of Malaysia, we will be in trouble," Liow told a conference on national security and the IS threat in Kuala Lumpur.

Nearly 100 Malaysians have gone to Syria and Iraq to fight with the jihadis, according to the police.

The anti-terrorism police unit has charged more than two dozen IS sympathisers in court.

On Monday, police arrested a 19-year-old student upon his return from Syria, where he was suspected of being involved in terrorism.

The suspect allegedly joined an al-Qaeda-linked terrorist cell in Syria in mid-2014.

- dpa