The police interrogated firebrand cleric Habib Rizieq Shihab for more than five hours yesterday, while about 2,000 of his supporters staged a street protest outside the Jakarta police headquarters.
The leader of the Front Pembela Islam (FPI), or Islamic Defenders' Front, was not arrested, but he told reporters that he has been ordered by police to return next Tuesday for further investigations.
He was questioned by investigators from the Special Crimes Directorate about his claims that the new series of rupiah banknotes featured symbols that were conceived during the Russian Revolution and are associated with communism.
Mr Rizieq remained defiant after his interrogation, demanding that the government remove the hammer-and-sickle pattern, which he was told was a security feature in the new notes.
"But there are thousands, millions of alternative images... Why the hammer and sickle?"
The 51-year-old ulama, or cleric, gained notoriety for leading a series of public rallies last year against Jakarta Governor Basuki Tjahaja Purnama - also known as Ahok - for allegedly insulting Islam.
But he now faces multiple allegations of blasphemy against other religions, as well as accusations of defaming Indonesian national symbols.
This was the second time in less than two weeks that he has been summoned for police investigation.
He was interrogated by the West Java police for more than six hours on Jan 12, over allegations that he had defamed the state ideology Pancasila and Indonesia's founding president, Sukarno.
The police are building their case against Mr Rizieq based on a two-minute video, which showed him saying that President Sukarno had written an earlier version of Pancasila that did not prioritise a belief in God.
There have been at least three other police reports lodged against him, including a complaint by a local Catholic group that accused him of making blasphemous comments about Jesus Christ.
It has been widely speculated in recent days that the police and prosecutors will officially declare Mr Rizieq a suspect and tender criminal charges against him soon.
This came after West Java prosecutors announced last Friday that they will also be interviewing Mr Rizieq over the same allegations.
The involvement of prosecutors at this stage of a probe typically signals a finalisation of indictments against a suspect, said lawyers.
The move also comes as dissent against the FPI grows louder across the country, with rallies against religious and racial intolerance being held in places such as Bandung in West Java, and Bali in recent days.
Mr Rizieq is not short of supporters, with an estimated 2,000 members of the FPI and other hardline groups gathering yesterday morning at the Masjid Agung Al-Azhar in Jakarta, to stage a street march in a show of solidarity.
The Masjid Agung Al-Azhar is the second-largest mosque in the capital and about 2.5km from the city's police headquarters.
The protesters took to the streets just before 9am local time and marched along the main thoroughfare to the Jakarta police headquarters, chanting anti-Ahok slogans and demanding Mr Basuki be jailed. He is running for a second term in February's gubernatorial election.
Mr Asep Syarifudin, who heads the Islamic Movement Alliance at Al-Azhar mosque, was one of the earliest to arrive for the rally.
"We will support ulama who are criminalised by anyone and we won't let anyone criminalise ulama," he told The Straits Times.