The police are looking into an alleged public protest on an MRT train last Saturday in which a group of activists was seen protesting against the detentions under the Internal Security Act (ISA) 30 years ago.

This follows a police report which was lodged against the group.

In 1987, 22 activists were arrested under Operation Spectrum for being part of what the Government called a Marxist plot aimed at overthrowing it.

The protest comes after some former ISA detainees launched a book last month titled 1987: Singapore's Marxist Conspiracy 30 Years On.

The group was seen riding a train on the North-South Line while holding copies of the book and wearing blindfolds in a silent protest.

They also pasted signs such as "Marxist Conspiracy" and "Justice for Operation Spectrum Survivors" on the train.

The Straits Times understands that the police report was made on Sunday.

Anyone with information on the incident can visit the website www.police.gov.sg/iwitness to submit it and all information will be kept strictly confidential, a police spokesman said.