Indonesian police said Wednesday they were probing reports that at least one demonstrator was killed in clashes that broke out in the capital Jakarta overnight after a rally opposed to President Joko Widodo's re-election.
Authorities clad in riot gear fired tear gas to disperse crowds from downtown Jakarta early Wednesday morning, as some demonstrators refused to leave the area and hurled fireworks and rocks at police.
Earlier, some protesters had set market stalls on fire, according to an AFP reporter on the scene, and a number of cars were set alight.
It was not immediately clear how many demonstrators or police may have been injured.
But National police spokesman Dedi Prasetyo said authorities were probing reports that a protester had been killed by a stray bullet, although he denied that the police had fired live rounds.
"We are still checking, but I need to reiterate that police officers were not equipped with live bullets," he told reporters.
About 20 people were arrested, he added.
A former special forces commander was earlier detained for trying to smuggle weapons into protests, according to the government.
A major commuter train station in the area had been temporarily shut, while roads were blocked off in parts of the sprawling city.
Some shopping malls, businesses and schools were also closed.
More than 30,000 troops had been deployed across Jakarta in anticipation of protests after official election results were published.
On Tuesday, Indonesia's election commission confirmed Widodo, 57, had beaten retired military general Prabowo Subianto for the presidency in a poll held on April 17.
Subianto has said he would challenge the results in court, and earlier warned that his claims of widespread cheating could spark street protests.
Several thousand people rallied in support of Subianto near the election supervisory agency office in the heart of the capital on Tuesday.
The protest ended peacefully, but then violent clashes broke out several hours later after some demonstrators returned to the scene.
Tensions have also spiked since police said last week that they had arrested dozens of Islamic State-linked terror suspects who had planned to cause chaos by bombing post-election protests.
Last month, a record 245,000 candidates ran for public office in Indonesia's elections, from the presidency and parliamentary seats to local positions -- the first time all were held on the same day.