Bukit Aman’s special branch division believes that foreign agents could have been behind the assassination of Kim Jong-nam, the estranged half-brother of North Korean leader Kim Jong-un.

“We cannot rule out the possibility. They could have been working on him for quite some time,” special branch director Fuzi Harun was quoted as saying by Channel News Asia.

Fuzi, however, said that this was just one of several possibilities.

He said his department was cooperating with other relevant agencies in the investigation, with the criminal investigation department taking the lead.

Jong-nam on Monday had reportedly tried to board a flight to Macau when he was assaulted, possibly with poison.

He sought help at the customer service counter at the airport but died on the way to the hospital.

Meanwhile, Reuters reported that Indonesia's foreign ministry has confirmed that a female national had been arrested in connection with the killing.

“Our embassy has verified the information received from Malaysian security authorities and based on preliminary data, the woman in question is an Indonesian citizen,” the foreign ministry said in a statement.

The Indonesian embassy has also requested consular access to the woman to provide legal assistance, it added.

Channel News Asia, quoting a senior police source, reported that the woman’s boyfriend, a Malaysian man, was also arrested in connection with the murder.

The woman, as well as the first suspect who carried a Vietnamese passport, were remanded for seven days in connection with the death.

The first suspect carrying the Vietnamese passport was arrested yesterday after she was identified from airport CCTV footage.