By Fergus Jensen and Johan Purnomo

JAKARTA (Reuters) - 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.

'COMMUNICATION'

Wiranto, the coordinating minister for political, legal and security affairs, told reporters the president had instructed him and other ministers to "receive" representatives of the protesters.

"I hope there will be a point of agreement," he said. "Let's not have a confrontation, but what is important is there's a communication."

Police are investigating the case against Purnama, who has apologized for the remarks. Widodo, a Muslim, has vowed not to interfere in any legal proceedings against Purnama, according to the Indonesian Clerical Council.

Many of the protesters wore white robes and Muslim caps and gathered at the central Istiqlal Mosque, the biggest mosque in the country, before they began moving toward the presidential palace.

There were smaller protests against Purnama in other cities including Surabaya, Makassar and Medan.

Critics say Widodo's government has not done enough to contain the religious and ethnic tension that is mounting ahead of a city governor election in February.

Purnama has a reputation as a tough reformer. He will compete for re-election against two Muslims - Agus Harimurti Yudhoyono, a son of former president Susilo Bambang Yudhoyono, and a former education minister, Anies Baswedan.

Ethnic Chinese make up just over one percent of Indonesia's 250 million people, and they typically do not enter politics.

There has been opposition to the hardliners on social media and some banners draped from an overpass called for respect of diversity.

"Your religion or ethnicity doesn't matter, as long as you can do something good for everybody," said one banner.

Indonesia suffered a series of Islamist militant attacks early in the last decade. In the most serious incident, 202 people were killed in bombings of a nightclub on the island of Bali in 2002.

An attack in Jakarta early this year by supporters of Islamic State raised fears of a new wave of violent militancy.

(Reporting by Fergus Jensen and Johan Purnomo; Additional reporting by Gayatri Suroyo, Fransiska Nangoy, Angie Teo and Wilda Asmarini; Writing by Eveline Danubrata; Editing by Michael Perry, Robert Birsel)