North Korean leader Kim Jong-un's half-brother has been killed in Malaysia, a government source said on Tuesday, sparking speculation over whether North Korea was behind a high-profile assassination.

Kim Jong-nam was assassinated on Monday in Malaysia, Yonhap news agency quoted the source as saying, without revealing any further details.

South Korea's cable TV broadcaster TV Chosun reported that Kim was killed at an airport in Malaysia after being attacked by two unidentified women with "poisoned needles". 

The suspects fled the scene and Malaysian police suspected North Korea was behind the killing. Repeated calls to South Korea's spy agency seeking comment went unanswered.

The assassination came as North Korean leader Kim Jong-un has been trying to consolidate his grip on power that he inherited upon the death of his father and long-time leader Kim Jong-il in 2011 amid growing international pressure over North Korea's nuclear and missile programmes.

Kim Jong-nam -- the eldest son of late leader Kim Jong-il -- had voiced opposition to his father's power succession to Kim Jong-un. He was born from his father's non-marital relationship with Sung Hae-rim, a South Korean-born actress who died in Moscow.

Kim Jong-nam had lived abroad for years after apparently falling out of favour with his father for attempting to enter Japan on a fake passport in 2001.

Kim's case would mark the most high-profile death under the Kim Jong-un regime since the execution of Jang Song-thaek in December 2013, the once-powerful uncle of the current leader.