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A woman was detained Wednesday in connection with the suspected killing of North Korean leader Kim Jong Un's half-brother, police said.

A man believed to be Kim Jong Nam died after falling ill at Kuala Lumpur's airport on Tuesday. South Korean officials believe he was approached by two women and then poisoned as he waited to board a flight.

The woman arrested Wednesday was carrying a Vietnamese passport identifying her as 28-year-old Doan Thi Huong, according to a statement by the Royal Malaysia Police.

She was identified from security footage and was alone when she was arrested, the statement added.

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Earlier, Malaysia's state news agency, Bernama, said the woman was from Myanmar, although it did not say how it knew her nationality.

Kim Jong Nam at Tokyo's Narita airport in 2001. Toshifumi Kitamura / AFP - Getty Images

The man who died at the airport was carrying documents identifying him as 46-year-old Kim Chol, according to Malaysian police.

However, lawmakers from South Korea, bitter enemy of the North, said that their intelligence agencies believe this was a false alias and that the man was in fact the half-brother of North Korea's dictator.

South Korea's National Intelligence Service (NIS) said Kim Jong Nam has been under a "kill order" since his half-brother took power in 2011, according to opposition politician Kim Byung Kee.

NIS officials believe two women approached Kim and poisoned him as he was waiting in line for a flight to Macau, according to the lawmaker, although he added they were waiting for the autopsy report.

The man who is thought to be Kim Jong Un's sibling fell ill and died en route to the hospital.

Two women fled the scene in a taxi, South Korean officials said, although it was not immediately clear whether either of them was the women who was reportedly arrested Wednesday.

Believed to be aged in his 40s, Kim Jong Nam is believed to have fallen out of favor with the regime in 2001 after he was caught trying to enter Japan under a fake passport, saying he wanted to enter Tokyo Disneyland.

His reported death comes days after North Korea declared its first missile test since the inauguration of President Donald Trump.

Earlier this month, South Korea said its secretive northern neighbor dismissed its minister of state security, who was a key aide to Kim Jong Un and ran the country's secret police.