Indonesian police fired tear gas to disperse demonstrators in downtown Jakarta early Wednesday after a rally opposed to President Joko Widodo's re-election, an AFP reporter said.
The country's election commission on Tuesday released official results that 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 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 Jakarta on Tuesday.
The protest ended peacefully, but police in riot gear later fired tear gas at some demonstrators who refused to leave the area and hurled fireworks and other objects at police.
Earlier, some protesters had set market stalls on fire.
It was not immediately clear if any demonstrators or police were injured in the clash.
More than 30,000 troops were deployed across the capital in anticipation of protests after the official election results were published.
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.