“What he said was not in line with the facts and discrediting an institution without facts and evidence is dangerous,” national police spokesman Dedi Prasetyo said on Friday in response to the charges.

However, campaigners derided the move.

“This is a blatant and ludicrous attempt to intimidate and silence Robertus for his peaceful criticism of the military,” Amnesty International Indonesia’s Executive Director Usman Hamid said in a statement.

“He is an academic who is guilty of nothing more than voicing his views over proposals to place senior military officers in positions of power within the government. The police must drop their baseless charges.”

The case centres on Robet singing a popular song at a weekly human rights protest in Jakarta last week with the lyrics altered in a way that allegedly made fun of the military. He has since apologised.

“It was a popular song during the 1998 student movement, which was meant to criticise the military then not now,” Robet said in a separate video released on social media before his arrest.

“I did not mean to insult the military as a profession or institution. For any misunderstanding, I do apologise,” he added.

Suharto’s three-decade military dictatorship – infamous for its eye-watering levels of corruption – crumbled in 1998 amid massive street protests as the collapsing economy was hit hard by the Asian Financial Crisis.

Indonesia has transformed into the world’s third-largest democracy since, but critics said Robet’s arrest highlighted the fragile state of freedom of speech in the country.

“This action is clearly aimed at creating fear to express freedom of speech,” Indonesian think-tank Institute for Criminal Justice Reform and Press Legal Aid Foundation said in a joint statement.

Several people have been charged under the legislation in recent years, including a woman accused of insulting the government over its apparent inability to control food prices.