Indonesian police deployed armored vehicles and armed personnel in the capital Jakarta ahead of a Friday protest planned by hardline Muslims groups against the governor, a Christian and the first ethnic Chinese in the job, over claims he insulted the Koran.
Police said dozens of social media accounts had been found "publishing provocative statements and images" and urging people to take violent action in the name of Islam against Governor Basuki Tjahja Purnama, better known by his nickname "Ahok", including calls to kill him.
"We have seen racially and ethnically divisive statements being spread online and there are indications many of them are anti-Chinese," said Jakarta police spokesman Awi Setiyono.
Ethnic Chinese make up just over one percent of Indonesia's 250 million people, who are overwhelmingly Muslim. Typically, Indonesian Chinese do not enter politics, but Purnama has been a close ally of President Joko Widodo for decades.
He was the deputy governor of Jakarta when Widodo was governor and took over when Widodo stepped down in 2014 to contest the presidency.
Critics say Widodo's government is doing little to contain the increasingly hostile rhetoric against Purnama from hardline Muslim groups. The mounting religious and ethnic tensions come ahead of next year's election for Jakarta governor in which Purnama has said he will be a candidate.
"This theater of hatred will continue if (Widodo) doesn't tackle it and Indonesia will be a different country with less tolerance and more persecution of minorities," said Andreas Harsono of Human Rights Watch.
Muslim groups have accused Purnama of blasphemy after he said his opponents had deceived voters by attacking him using a verse from the Koran. Police are investigating the case against Purnama, who has apologized for the remarks.
Widodo has urged protesters to demonstrate peacefully.
He has also vowed not to interfere in the legal proceedings against Purnama, according to the Indonesian Clerical Council, a Muslim group.
"The president has said he has instructed (police) to process the investigation and that he will not intervene in this matter," council member Ma'aruf Amin told reporters after meeting Widodo earlier this week.