JAKARTA (Reuters) - Indonesian police have arrested at least 20 people accused of provoking riots in Jakarta following official results showing President Joko Widodo had been re-elected, a police spokesman said on Wednesday.

Television footage on Wednesday showed smoke billowing from behind dozens of protesters who were dancing in the street in the Tanah Abang district of central Jakarta.

A separate crowd in front of the election supervisory body threw rocks at police, a Reuters witness said.

The General Election Commission (KPU) on Tuesday confirmed unofficial counts by private pollsters in the April 17 election, which gave Widodo a 55.5% share of votes against 44.5% for his opponent, former general Prabowo Subianto.

Widodo won more than 85 million votes of a total of 154 million cast in the world’s third-largest democracy, but Prabowo told reporters he believed there had been widespread cheating and about 1,000 supporters gathered in Jakarta a day earlier.

On Monday, an election supervisory agency dismissed claims of systematic cheating, citing a lack of evidence. Independent observers have said the poll was free and fair.

Protests that started peacefully on Tuesday turned violent in the evening, forcing police to fire tear gas to disperse the crowd. Cars parked near an apartment housing the police’s mobile brigade were set ablaze, media reported.

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“As of now, police have arrested more than 20 people we thought were the provocateurs and who did other crimes,” said police spokesman Dedi Prasetyo.

Prasetyo said police were checking on reports of casualties, but stressed that security officers on the ground, which include military personnel, were not equipped with live bullets.

News website Tirto reported a man died of bullet wounds in Tanah Abang, quoting a doctor at a hospital near the site.

Indonesian authorities have said 40,000 police and army personnel were on duty across Jakarta in a bid to maintain security.