SEOUL (REUTERS) - South Korea's prime minister will preside over a national security council meeting on Wednesday morning (Feb 15) to discuss the suspected murder of the North Korean leader's estranged half-brother in Malaysia, his office said.

Mr Kim Jong Nam, the half-brother of North Korean leader Kim Jong Un, was found dead in Malaysia, according to Malaysian police on Tuesday.

US government sources have told Reuters they believe he had been murdered by North Korean agents. A South Korean official also said they believed he had been murdered, without giving further details.

Mr Kim Jong Nam, who was estranged from the young North Korean leader, was known to spend a significant amount of his time outside North Korea and had spoken out publicly against his family's dynastic control of the isolated state.

South Korea is acutely sensitive to any sign of potential instability in its impoverished and nuclear-armed neighbour, with which it remains technically in a state of war.

Malaysian police said the dead man, 46, held a passport under the name Kim Chol. Mr Kim Jong Nam has been caught in the past using forged travel documents.

Malaysian police official Fadzil Ahmat said on Tuesday that the cause of Mr Kim's death was not yet known, and that a post-mortem would be carried out. The man had been planning to travel to Macau on Monday when he fell ill at the low-cost terminal of Kuala Lumpur International Airport (KLIA), Mr Fadzil said.

The US government sources said it was possible that Mr Kim Jong Nam had been poisoned.