JAKARTA -- Indonesian police alleged a "systematic" plot to undermine security in Jakarta after protests against the results of the recent presidential election turned violent early Wednesday morning, reportedly leading to several deaths and scores of injuries. President Joko "Jokowi" Widodo pledged to take firm action against the violence.
Police said that 257 people had been arrested as of Wednesday night. Clashes between security forces and protesters continued into the early hours of Thursday.
National Police spokesperson Muhammad Iqbal said on Wednesday that rallies in front of the Election Supervisory Body, or Bawaslu, office in Central Jakarta started out peacefully on Tuesday afternoon.
Supporters of opposition leader Prabowo Subianto voiced their rejection against the official tally issued by the General Elections Commission earlier that day showing incumbent President Joko Widodo won with 55.5% of the vote against Subianto's 44.5%.
But after the protesters dispersed on Tuesday night, a separate crowd arrived near midnight and clashed with security forces from the police and military for a few hours. An additional crowd of 200 people attacked a police compound in West Jakarta near dawn, torching more than a dozen cars parked in the front yard.
"We don't know where they're from," Iqbal said at the police headquarters. "They committed anarchy and provoked officers ... hurling stones, Molotov cocktails and firecrackers at officers. They were very brutal."
"We think the early morning incidents are not spontaneous, but have been staged," he said.
He added that police have arrested around 70 people from among the rioters, and that they likely came from outside Jakarta, with some found to be carrying envelopes containing rupiah notes -- suggesting that they had been paid. Police also seized an ambulance carrying stones and other items believed to have been prepared to attack security personnel.
Jakarta Gov. Anies Baswedan, a member of the opposition party, said six people were killed and 200 were hospitalized, suggesting without clarification that all were victims of the clashes early Wednesday morning. Iqbal said police were still checking the casualty and injury reports.
Widodo spoke on Wednesday, saying he will "not tolerate ... will not give space to rioters who will damage" the country, and that the military and police will "take firm action in accordance with the prevailing rules of law."
Subianto called for restraint on all sides. "I appeal to all the people who convey their aspirations, the police, the military and all parties to exercise restraint, so as not to commit physical violence," he said. "The violence [like] last night should never happen again."
Despite the rising tensions, the stock market remained unfazed, with the Jakarta Composite Index ending the day down 0.2%.
The bitter election pitted Widodo against Subianto, a former general, who has said he plans to challenge the official result from Indonesia's election commission with the Constitutional Court. Subianto said on Tuesday that he and his running mate, Sandiaga Uno, "reject the result" and "will make all legal efforts to defend the people's sovereignty."
Iqbal said police have identified some social media accounts linked to "certain groups" that have purposefully spread disinformation related to the riots and protests to further muddy the situation.
He said that among the false viral messages being circulated is one about police attacking a mosque while chasing rioters, and that security forces from mainland China took part in the Indonesian police's crackdown against protesters.
Separately, Presidential Chief of Staff Moeldoko said three people have been arrested for alleged gun smuggling related to the aftermath of the election. He said that security forces have been instructed against using metal bullets to secure the rallies and were equipped only with shields and tear gas, while some had rubber bullets.
"So a narrative has been specifically manufactured that whenever [a protester] gets shot, it is as if it was by the military or the police, so as to provoke rioting," Moeldoko said in a television interview, adding that the unidentified group also targeted some government officials for an attack.
"There are systematic attempts from certain groups, outside the terror cells, to ride on this situation," he said.
Police said last week that they had detained 29 people suspected of plotting strikes in May alone -- with all of them associated with Jamaah Ansharut Daulah, or JAD, the largest Indonesian pro-Islamic State cell.
Tarakan Hospital in Central Jakarta, one of several hospitals reportedly treating the injured, said it had two dead victims and 80 injured people from the clashes, according to local news portal tirto.id.
The security situation in the capital returned to normal as of Wednesday afternoon, with thousands of Subianto's supporters again appearing outside the Bawaslu office near a main business district in Central Jakarta to hold a peaceful rally.
But security personnel remained on high alert, with 34,000 officers from the military and police dispatched across Jakarta to secure the city.
Roads outside the Bawaslu office, as well as some roads and rail stations near the attacked police compound, remained closed as of Wednesday afternoon. Many offices in Jakarta were also closed, with employees told to work from home to avoid other possible clashes.
Nikkei staff writer Shotaro Tani in Jakarta contributed to this article.