The two women accused of the assassination of Kim Jong-nam, the estranged brother of the North Korean Leader, have been ordered to submit their defence to a court in Malaysia after the judge ruled there was enough evidence against them for the trial to proceed.

Siti Aisyah, from Indonesia, and Doan Thi Huong, from Vietnam, are accused of orchestrating the murder of Kim Jong-nam in Kuala Lumpur airport in February 2017, by smearing toxic nerve agent VX on his face as he waited to board a flight to Macau. He died within 20 minutes.

The defence had hoped that the hearing at Shah Alam High Court in Kuala Lumpur would see Siti and Doan acquitted of all charges, but the judge ruled that the trial should continue as there was “credible” evidence against them. The pair face a mandatory death sentence if they are found guilty of the murder.

Judge Azmi Ariffin accepted the prosecution’s case that the women, in common intention with four individuals still at large, had caused the death of Kim. “I must therefore call upon them to enter their defence on their respective charges,” he added.

He accepted that it could have been a “political assassination” but said he could not rule out that there had been a “well-planned conspiracy” between the two women and the North Korean operatives.

The judge called into question the argument that the pair had been carrying out a prank, saying it was unlike any prank he had researched, and said it needed to be explained why Doan had rushed to the bathroom afterwards to wash her hands. His order will extend the trial by at least another two months.

The women, who will testify under oath as part of their defence, looked shocked at the ruling. Siti’s lawyer Gooi Soon Seng told reporters: “We are deeply disappointed with the ruling ... We will do our best at the defence stage.”

Both women have pleaded not guilty to conspiring with the North Korean state to carry out the killing. Their lawyers argued that they were duped into thinking they were playing a prank for a reality TV show and did not know they were poisoning Kim.

Over the course of the trial, which has lasted nine months so far, the prosecution laid out a plot reminiscent of “James Bond”, claiming Siti and Doan had been recruited by four North Korean operatives and trained as assassins to carry out the poisoning with VX. The poison is known as the “most potent of all nerve agents” and classified by the United Nations as a weapon of mass destruction.

The prosecution’s case rests on airport CCTV footage which showed Doan, wearing a jumper bearing the letters “LOL”, approaching Kim from behind and putting her hands over his face. She then ran off. Another figure spotted walking away from the scene was later identified as Siti.

However Gooi Soon Seng accused the prosecution’s investigation of being based only on “circumstantial evidence” and having failed to demonstrate a motive for the murder.

The defence for both women argued that they were innocent scapegoats in a state-sponsored political killing and that the real culprits were the North Korean operatives, who fled the country after the murder and have yet not been apprehended.

Both women say they had been approached by North Korean operatives in early 2017 while working as escorts, Doan in Hanoi and Siti in Kuala Lumpur. They claim they were both fed a similar story: that they had been selected to take part in a Japanese comedy Youtube show, where they would perform pranks by smearing lotion of people’s faces.

Siti said she was paid hundreds of dollars to carry out the prank at various malls in Kuala Lumpur as practice before she was brought to the airport on 13 February, and shown Kim as the next target for the TV show. Both Siti and Doan deny knowing who he was.

Kim had originally been the favoured child to take over from his father, Kim Jong-il, but became estranged from the family after an incident in 2001, when he was he was arrested trying to get into Japan on a fake Dominican passport with the Mandarin alias “fat bear”, admitting later he had been trying to visit Disneyland in Tokyo.

The incident was said to have caused embarrassment to Kim Jong-il, who cut ties with his son and refused to let him back to Pyongyang. Kim Jong-nam instead settled in the Chinese gambling enclave of Macau. He expressed little desire to return to North Korea, and angered his younger brother, who took leadership in 2011, by saying that the world would view Kim Jong-un’s leadership as a “joke”.

However, Kim was reported to have become increasingly fearful and paranoid in the past few years, fearing retribution from his brother. The court case revealed he had been carrying 12 doses of an atropine, an antidote to VX nerve agent, in his bag at the time of his death.