The first suspect was caught at the airport -- a 29-year-old woman with Vietnamese travel documents under the name Doan Thi Huong. Malaysian police suspect that a total of four men and two women were involved, according to foreign news reports.

Kim Jong-nam -- the eldest son of late former leader Kim Jong-il -- was killed at an airport in Malaysia on Monday after allegedly being attacked with poison by two women, according to South Korea's spy agency.

Singapore's Channel NewsAsia reported that police arrested a Malaysian man, known as the boyfriend of the second female suspect, in connection with the case. The report is not confirmed as Malaysian police have yet to make an announcement.

South Korea's intelligence service said that the murder of Kim Jong-nam has been a "standing order" issued by Kim Jong-un since he inherited power in late 2011 following the sudden death of his father.

The 46-year-old was at the airport to take a flight to Macau when he was attacked by two "Asian" women, he died en route to a hospital.

The South Korean government confirmed Kim’s death, but stopped short of saying that North Korea was behind it, adding that it is awaiting the results of Malaysian police's probe.

"If Kim Jong-nam's murder was carried out by North Korea, the North's leader would have been aware of that," said an official at Seoul's unification ministry.

Kim Jong-nam was once viewed as the heir apparent, but he had been living in foreign countries for years after apparently falling out of favor with his father for attempting to enter Japan with a fake passport in 2001.

The latest case marked 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 incumbent leader.

Experts said that the assassination is seen as the North Korean leader's move to strengthen his reign of terror by eliminating any potential challenge to his one-man rule. (Yonhap)