Over 150,000 Indonesian Muslims have protested in Jakarta, calling for the city's Christian governor Ahok to be jailed.
Tens of thousands of Muslims poured into central Jakarta on Friday to protest against the city's governor, a Christian accused of insulting the Koran, fuelling tension that has alarmed Indonesian President Joko Widodo.
Widodo has blamed "political actors" for exploiting the popular fury over Governor Basuki Tjahaja Purnama to destabilize his government. Underlining those concerns, police announced on Friday that 10 people had been detained for alleged treason.
A sea of white-clad protesters had built up around the National Monument by mid-morning and, with no more room there, the roads around it filled up with protesters chanting, praying and carrying banners demanding that Purnama be jailed.
Some reports put the number of protesters at more than 200,000.
When asked what his message was for the military and police, Widodo told reporters at an event some distance from the rally: "Stand guard so that everything runs safely."
National news agency Antara said 22,000 police personnel would be deployed to avoid a repeat of violence that flared during a protest led by hardline Islamists last month when more than 100 people were injured in clashes with police.
Jakarta Governor Purnama, an ethnic Chinese popularly known as Ahok and a long-time ally of the president, is running for re-election in February against two Muslim candidates.
The contest has generated high political tension for weeks, with rumors of plots to undermine Widodo and scupper his chances of winning a second term in 2019.
Widodo is a long-time ally of Purnama. Police have warned against attempts to destabilize the government.
Police spokesman Rikwanto told a news conference that 10 people who he identified only by their initials had been detained before dawn, citing articles of the criminal code that cover conspiracy and acts of treason. Two of them were charged under the law of information technology for hate speech.
"They have now been detained and are undergoing investigation," said Rikwanto, who goes by only one name.
Indonesia has the world's biggest Muslim population but recognizes six religions and is home to dozens of ethnic groups, some of which follow traditional beliefs.
Purnama is being investigated over comments he made about his opponents' use of the Koran in campaigning. He denies wrongdoing but has apologized for the remarks.
Police on Thursday handed over a dossier from their investigation of his comments to prosecutors, who are expected to take the case of alleged blasphemy to court in coming weeks.
"This gathering is an expression of Muslims being united as one people, one body," said Salist Nursolikhah, 49, who flew into Jakarta from the city of Yogjakarta to join the rally.
"It's not against a particular person because of his ethnicity. We are only against his action," she said.
Simmering religious and ethnic tension last month prompted Widodo to rally top military, political and religious figures in a sign of unity amid fears of attempts to undermine the stability of his government.
The Jakarta government has put up billboards on major roads calling for national unity and displaying pictures of independence heroes who fought against colonial rule.
Purnama is popular with many for pushing through tough reforms to modernize the traffic-plagued capital.
But opinion polls have shown him slipping into second place in the race for re-election as governor, a position that Widodo himself, who is popularly known as Jokowi, used as a stepping-stone to the presidency.
"Jokowi's handling has been inadequate because it looks like he's defending Ahok," said protester Rini Pupitasari. "We will keep demonstrating until he is detained. But we will do so peacefully."