A Vietnamese woman charged with murdering the North Korean leader's half-brother has lost her bid for release in Malaysia, days after her Indonesian co-accused was freed.

Doan Thi Huong broke down in tears as a prosecutor told a court the attorney-general in Malaysia had refused to drop a murder charge against her.

She has been on trial for a year-and-a-half over the 2017 assassination of Kim Jong-nam at Kuala Lumpur airport that shocked the world.

On Monday a murder charge was unexpectedly withdrawn against the Indonesian woman accused alongside her, Siti Aisyah, raising hopes that Ms Huong might also be freed imminently.

Speaking through tears, Ms Huong told reporters in court: "I am depressed. I am innocent ... I want my family to pray for me."

The pair had always denied murder, saying they were tricked by North Korean spies into carrying out the Cold War-style killing using a highly toxic nerve agent, and believed it was a prank for a reality TV show.

Their lawyers presented them as scapegoats and said the real killers were four North Koreans, who were suspected of being the masterminds behind the plot but fled Malaysia shortly after the killing.

The prosecutor did not give reasons why charges were not being dropped for Ms Huong, 30, who is now the sole defendant on trial for Mr Kim's murder and could face death by hanging if convicted.

Indonesia had mounted a sustained diplomatic offensive to get Ms Aisyah freed, while Vietnam had only stepped up pressure since the Indonesian woman's release this week.

Siti Aisyah smiles as she arrives from Malaysia at Halim Perdana Kusuma airport in Jakarta, Indonesia

During the trial, some of the evidence against Ms Huong had seemed stronger.

Airport CCTV footage shown in court captured her approaching Mr Kim, placing her hands on his face and then running away.

Ms Aisyah was only seen as a blurred figure fleeing the scene of the crime.

The trial began in October 2017 but there had been no hearings since August last year when the prosecution finished presenting its case.

Proceedings were scheduled to resume on Monday with Ms Huong testifying, but the unexpected release of her co-accused led to the trial being adjourned so the Vietnamese suspect could also seek her freedom.

But now, lead prosecutor Muhammad Iskandar Ahmad has told the High Court in Shah Alam, outside Kuala Lumpur, that the attorney-general had ordered the case against Ms Huong to proceed.

Doan Thi Huong has been on trial for a year and a half over the 2017 assassination of Kim Jong Nam

The judge said Ms Huong was not well enough to continue with the trial today and adjourned proceedings until 1 April.

A murder conviction carries a mandatory penalty of death in Malaysia. The government vowed last year to scrap capital punishment, but has indicated recently it may backtrack on the plan.

Vietnam had increased pressure on Malaysia to release Ms Huong, with the country's foreign minister this week pressing his Malaysian counterpart on the issue and the justice minister writing to the attorney general.