Kanhaiya Kumar, the president of the JNU students' union and an activist of a Left-linked group, was arrested by police in plainclothes, charged with sedition and conspiracy, and sent to custody for three days.

Policemen swarmed the JNU campus all day as they searched for more students suspected to be involved in the protest held on Tuesday to mark the death anniversary of Afzal Guru.

Anti-India slogans were allegedly raised during the event titled "The country without a post office", which featured an exhibition and a protest march. The BJP's student wing ABVP and a party lawmaker reported the event to the police.

Home Minister Rajnath Singh warned of "stringent action" against the organisers of the protest. "Anyone who raises anti-India slogans or tries to put a question mark on nation's unity and integrity will not be spared," he said.

Education Minister Smriti Irani said: The nation can never tolerate any insult to mother India."

After Kanhaiya's arrest, teachers and students protested outside the Vice Chancellor's office, demanding to know why students were being treated like "terrorists" and picked up from campus by plainclothesmen. A rival group of students belonging to the ABVP protested near the India Gate in the heart of Delhi.

"JNU has always been a university where there has been a vibrant culture. Excessive police action is uncalled for and has worsened the situation," professors said in a statement.

Left parliamentarian Sitaram Yechury commented in a tweet: "What is happening in JNU? Police on campus, arrests and picking up students from hostels. This had last happened during Emergency."

The university claims it cancelled permission for the Afzal Guru event, which was allegedly pitched as a cultural function. Vice-Chancellor Jagdeesh Kumar has called it an act of indiscipline.