SINGAPORE - The police have questioned at least one of the people involved in an alleged protest on an MRT train on June 3.

Mr Sean Francis Han, 22, who is also an activist and the editor of wakeupsg.com, was seen arriving at the Cantonment Police Complex around 9.30am on Monday (June 12).

Speaking to The Straits Times after he left the complex and the police had finished interviewing him at about 12pm, he said he did not know if there were any charges against him or the outcome of the questioning.

"I believe it's something to do with the police report made, so it's part of their due diligence. I tried asking but he said he couldn't tell me the reason," he said.

The activist added that he was not sure when the rest of the group involved in the alleged protest would be questioned by the police.

A police spokesman had earlier said that they were looking into the matter.

On June 3, the group of about seven were seen protesting against the detentions under the Internal Security Act (ISA) 30 years ago.

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

In May this year, some former ISA detainees launched a book titled 1987: Singapore's Marxist Conspiracy 30 years On.

The alleged protestors were seen riding a train on the North-South Line while holding copies of the book and wearing blindfolds in a silent protest. Social activist Jolovan Wham had also posted pictures of it on Facebook.