Vietnamese suspect Doan Thi Huong, right, arrested in the death of Kim Jong Nam, is escorted by police officers as she leaves a court house in Sepang, Malaysia. Picture: Vincent Thian/AP

Kuala Lumpur – Two women accused of killing the estranged half-brother of North Korea's leader made their second court appearance on Thursday wearing bullet-proof vests, but the hearing into the Kuala Lumpur airport assassination was postponed until May.

Siti Aishah, 25, from Jakarta, Indonesia, and Doan Thi Huong, 28, from rural northern Vietnam, face the death penalty if convicted of killing Kim Jong Nam.

The two women allegedly smeared Kim's face with the toxic VX nerve agent, a chemical described by the United Nations as a weapon of mass destruction, at the Kuala Lumpur International Airport on Feb. 13.

Thursday's scheduled hearing for the prosecutors' request that the two women be tried jointly and for the case to be transferred to a higher court was deferred to May 30.

Lead prosecutor Muhamad Iskandar Ahmad said more time was needed to collect documents from several departments.

The two suspects were brought separately to the heavily guarded Sepang courthouse, about an hour's drive from capital Kuala Lumpur.

The women were charged on March 1 along with four men, who Malaysian police have identified as North Koreans who left Kuala Lumpur for Pyongyang on the day of the killing. An Interpol red notice has been issued for the four.

Aishah and Huong have told their respective diplomats that they were unwitting pawns in an assassination that U.S. officials and South Korean intelligence have said was organised by North Korean agents.

Malaysia's investigation into the murder sparked a diplomatic row with North Korea, resulting in travel bans on both sides and damaging the countries' historically close ties.

The travel bans were lifted last month after a deal was struck allowing Kim Jong Nam's body to be returned to North Korea and securing the release of nine Malaysian citizens held in Pyongyang.

Three North Koreans wanted for questioning in the murder were also allowed to leave Kuala Lumpur as part of the swap.