JAKARTA: Thousands of white-clad Muslims streamed towards a central Jakarta park on Friday, gathering for a rally expected to draw more than 100,000 Indonesians demanding the arrest of the capital's governor, a Christian accused of insulting the Koran.

National news agency Antara said 22,000 police personnel would be deployed to avoid a repeat of the violence that flared during a protest led by hardline Islamists last month when more than 100 people were injured in clashes with police.

Muslim groups accuse Governor Basuki Tjahaja Purnama of insulting the Koran, though they have pledged that Friday's demonstration will be peaceful.

Purnama, popularly known as Ahok, is running for re-election in February against two Muslim candidates.

The race for the governorship has generated high political tension, and rumors of plots to undermine President Joko Widodo and scupper his chances of winning a second term in 2019.

Widodo, a long-time ally of Purnama, has blamed "political actors" for taking advantage of the popular fury among Muslims over Purnama to further their own ends, and the police have warned against attempts to destabilize his government.

Local media said on Friday that eight people had been detained for alleged treason. Police officials were not immediately available to comment on the reports, and Widodo declined to comment when asked by reporters.

Protesters began moving from the hulking Istiqlal mosque towards the National Monument in the center of the city at around 5 am, after morning prayers.

"We are expecting over 100,000 participants," Jakarta police spokesman Argo Yuwono said late on Thursday. "There is enough security so the public need not worry. We hope everything will proceed according to the agreement with the protesters."

FEARS FOR POLITICAL STABILITY

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, an ethnic Chinese Christian, 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 their investigation dossier to prosecutors, who are expected to take the case of alleged blasphemy to court in the 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.

Police helicopters last week dropped leaflets over the capital warning of harsh penalties if the upcoming rally turned violent.

The Jakarta government has also put up billboards on major roads calling for national unity and displaying pictures of independence heroes who fought against colonial rule.

The Australian foreign ministry and the US embassy in Jakarta issued security notices urging nationals to avoid the demonstration.

Purnama is popular with many for pushing through tough reforms to modernize the country's traffic-plagued capital city.

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."