HANOI (AFP): Vietnam on Tuesday (March 12) asked Malaysia to free the Vietnamese woman charged with assassinating the North Korean leader's half brother in Kuala Lumpur, a day after her Indonesian co-accused was suddenly released.

Vietnamese citizen Doan Thi Huong is on trial for murder in Malaysia for the brazen Cold War-style killing of Kim Jong-nam, the half brother of Kim Jong-un, in a busy Kuala Lumpur airport in 2017.

Huong was accused alongside Indonesian Siti Aisyah, who was freed on Monday by a Malaysian court where the women were being tried.

Vietnam's Foreign Minister Pham Binh Minh called his Malaysian counterpart on Tuesday asking Huong to be released as well, according to state media.

"(He) asked Malaysia to ensure a fair trial, and to set free Doan Thi Huong," Voice of Vietnam radio reported Tuesday after Minh's call with Malaysian Foreign Minister Datuk Saifuddin Abdullah.

Huong is set to appear in court on Thursday (March 14) after her lawyers asked the Attorney General to withdraw her murder charge. Prosecutors may decide then inform the court whether the application is successful.

The call from Vietnam's foreign minister was an unprecedented public request from Hanoi, which generally does not get involved in criminal cases involving its citizens overseas.

Vietnam provided legal counsel to Huong, but has refrained from publicly lobbying for her release until Tuesday.

Siti's sudden release prompted questions about interference in Malaysia's justice system, particularly after the Indonesian government revealed that it had lobbied Kuala Lumpur on the case.

Malaysian Prime Minister Tun Dr Mahathir Mohamad said Tuesday the decision was in line with "the rule of law".

Huong and Siti have consistently denied the murder charge and have said they were tricked into carrying out the killing using a toxic nerve agent for what they thought was a prank.

The women's lawyers say the real killers are four North Koreans – formally accused of the crime alongside the women – who fled Malaysia shortly after the assassination.

South Korea accuses the North of plotting the murder of Kim, an estranged relative of Kim Jong Un who was once seen as heir apparent to the North Korean leadership. Pyongyang denies the accusation. – AFP