Tens of thousands of hardline Muslim protesters in Indonesia rallied outside the presidential palace on Friday to demand the resignation of the governor of the capital, Jakarta, who they said had insulted the Koran.

Indonesia is the world’s most populous Muslim country, where many people follow a moderate form of Islam. While hardliners have launched occasional agitation in the past, protests on such a large scale have been rare.

The atmosphere in Jakarta was tense and some companies asked employees to work from home, access to business districts was restricted and embassies urged caution.

Truck loads of soldiers and police, some equipped with rifles, were on patrol and others secured shopping malls. A total of about 18,000 security personnel are expected to be deployed in the sprawling city of 10 million, police said.

The protesters, led by a group called the Islamic Defenders Front, are calling for Jakarta governor Basuki Tjahja Purnama, a Christian and the first ethnic Chinese in the job, to be jailed for blasphemy.

They say he insulted the Koran by dismissing a political attack by his opponents who urged Muslims not to vote for Purnama, who is popularly known as Ahok, by citing a verse from the Koran.

“He is not Muslim but he humiliated the Koran,” protester Muhammad Said told Reuters.

“Don’t refer to anything in the Koran, especially interpreting it incorrectly … I call on God to jail him.”

Protesters chanted “Hang Ahok!” and “God is greatest”, waved placards and sang the national anthem.

Some threw water bottles at police guarding the palace but apart from that there was no violence.

Purnama was not available for comment. His spokeswoman said he went to check construction of a sidewalk in north Jakarta.

Purnama served as deputy to President Joko Widodo when Widodo was city governor from 2012 to 2014, and has long been seen as an ally of the president.

On Friday, Widodo visited a rail construction project at the capital’s airport, the presidential palace said in a statement.

Read More: reuters