JAKARTA - Security officers were out in force on Friday (June 14) to prevent a repeat of last month's riots in Jakarta, as the pre-trial hearing for the challenge mounted by defeated presidential candidate Prabowo Subianto began against the April 17 election results.

The former army general, who has now lost the presidential race twice to Mr Joko Widodo, is once again headed to court armed with charges of electoral fraud, in a last-ditch attempt to overturn the election results, just as he did after the 2014 polls.

Official results released by the Election Commission (KPU) on May 21 handed President Joko and his vice-presidential pick, Dr Ma'ruf Amin, the win, with 55.5 per cent of the votes to his rival's 44.5 per cent, but Mr Prabowo has refused to concede defeat.

He claims that he and running mate Sandiaga Uno won 52 per cent of the votes, and alleges fraud by his opponent and the election authorities.

The pre-trial hearing on Friday, with the ruling expected later in the day, will determine whether the court moves forward with the lawsuit. If it does, judges will likely hear evidence from June 17 to 21. A ruling, which is final and binding, is expected to be out on June 28.

The four men who ran in the presidential poll are not expected to be present for the hearing.

Police and the Indonesian military (TNI) have heightened security around the courthouse, and will be putting up traffic diversions in the vicinity.

Jakarta police chief Gatot Eddy Pramono told reporters: "We are coordinating with TNI, the Jakarta administration, and the court's security force in deploying 12,000 personnel around the court."

He added that up to 48,000 security officers are ready to be deployed in the capital if needed. In addition, about 500 traffic police officers will be on duty around the courthouse.

Jakarta is on alert after it was rocked just weeks ago by a short-lived burst of chaos, when street protests mounted by groups rejecting the official vote count flared into two days of widespread unrest around the capital. It led to the deaths of eight people and left more than 700 injured.

Concerns have been high that yet another round of protests could break out as the court case unfolds.

Mr Prabowo on Tuesday urged his supporters to stay away from the vicinity of courthouse during the hearing, stressing that he and Mr Sandiaga "have committed to peaceful and non-violent actions".

"We certainly do not wish for any kind of riot in this country. That is not how we solve problems here," he said in a video posted on his Facebook page. "That is why Sandiaga Uno and I hope that all our supporters remain calm, cool, peaceful and optimistic without forgetting the kinship and kindness that binds us all."

Mr Prabowo had, in a meeting with vice-president Jusuf Kalla, last week vowed that his key supporters would refrain from organising mass protests.

"I plead with all of you to trust us," he said in his Facebook video. "If you sincerely support (us), I plead that you do not surround the Constitutional Court... There is no need for masses of people, and this is to avoid further lies, misrepresentation and other provocateurs."

He added: "We must trust the judges. Whatever the decision will be, we must accept it calmly and maturely, and prioritise the interests of this nation and its people."

In the past few days, there has been a flurry of action on all sides, with the various camps preparing evidence, and trading barbs. Mr Joko's camp has submitted 18 pieces of evidence to the court, and assembled a team of more than 30 lawyers for the hearing, while the KPU on Tuesday sent trucks to the courthouse bearing 272 containers of evidence, including originals and copies of vote tally forms and minutes, to support its official count.

KPU commissioner Hasyim Asy'arei said the commission was ready to refute all charges of fraud aimed at it. Among other things, Mr Prabowo's camp has claimed that there were data entry errors of votes, and irregularities in the official voter roll.

Meanwhile, Mr Prabowo's team added yet more allegations to their lawsuit on Tuesday, with legal team head Bambang Widjojanto saying that the revisions contain crucial information that could disqualify Mr Joko and Dr Ma'ruf from the polls.

The claims are that there were irregularities in Mr Joko's campaign fund report, and that Dr Ma'ruf violated the law by keeping his positions in state-owned enterprises. The cleric was still registered as chairman of the syariah supervisory board at BNI Syariah and Bank Syariah Mandiri.

"A presidential or vice-presidential candidate must terminate their employment at any state-owned enterprise. We have looked into this multiple times, and we are sure this is a very serious violation," said Mr Bambang.

Mr Hasyim of the KPU said in a written statement that Dr Ma'ruf's position at the two banks was not against election law, as the two banks are only subsidiaries of state-owned banks BNI and Bank Mandiri.

"A subsidiary is different from a state-owned enterprise because the legal status and the financial state of the subsidiary is separate from the state-owned enterprise," he said, pointing out that Ms Mirah Sumirat, a candidate in Mr Prabowo's Gerindra party who contested April's legislative polls, was also an employee at a subsidiary of a state-owned enterprise.

On Thursday, as time drew closer to the pre-trial hearing, there were fighting words from both camps.

Mr Dahnil Anzar Simanjuntak, a spokesman for the Prabowo campaign team, said that the lawsuit represents the interests of the public.

"This concerns the rights of the people who have been cheated, based on valid proof. So we would like to emphasise that this court challenge is not just for Prabowo-Sandi. It is also for a healthy democracy," he said.

Meanwhile, Mr Joko's team was undaunted.

Campaign team spokesman Ace Hasan Syadzily told reporters: "We are very optimistic that we can crush the arguments they have submitted."