North Korean leader's brother
North Korean leader's brother Kim Jong NamReuters

North Korean leader Kim Jong Un's estranged half-brother was murdered in Malaysia on Tuesday and the United States strongly believes that Pyongyang agents were behind the act, according to Reuters reports.

The American authorities are yet to determine exactly how Kim Jong Nam was murdered, Reuters sources said. 

North Korea test-fires ballistic missile, as US President Donald Trump prepares to act

South Korea's foreign ministry said that it could not confirm the reports of Kim Jong Nam's murder. The North Korean leader's brother reportedly spent a considerable amount of time outside of North Korea and had also publicly denounced his family's dynastic control of the isolated nation.

The Malaysian police in a statement had said that they found a dead man, aged 46, who held a passport under the name of Kim Chol. The North Korean leader's brother has been caught using forged travel documents in the past too.

Malaysian police official Fadzil Ahmat said that the cause of Kim's death is not yet known and that his body has been taken for post mortem. "So far there are no suspects, but we have started investigations and are looking at a few possibilities to get leads," Fadzil told Reuters.

The official added that Kim had been planning to travel to Macau on Monday when he fell ill at the terminal of Kuala Lumpur International Airport (KLIA). "The deceased ... felt like someone grabbed or held his face from behind. He felt dizzy, so he asked for help at the ... counter of KLIA," Fadzil said.

Kim was then taken to an airport clinic where he repeatedly complained of feeling unwell, the authorities then decided to take him to a hospital. He died in the ambulance on his way to Putrajaya Hospital, according to Fadzil.

Although details of Kim Jong Nam's murder are not clear yet, if it is confirmed as an assassination, then it would be the latest one in a string of killings of those who are considered a threat to the authority of North Korean leaders, a US official told Reuters on condition of anonymity.

There was no response to the murder from Washington, which faces a tough challenge from North Korea over its nuclear arms testing. The North Korean nation earlier this week had announced that it had successfully conducted a ballistic missile test capable of carrying nuclear warheads.