MALAYSIAN police have formally identified Kim Jong Nam as the victim of a fatal nerve agent attack at Kuala Lumpur’s airport.

It is an expected but significant development in a case which has broken down the once-warm ties between North Korea and Malaysia.

Kim is the estranged half-brother of North Korea’s ruler Kim Jong Un, and the North has refused to acknowledge he was the victim of the February 13 killing.

Instead, North Korea refers to him as Kim Chol, the name on the passport Kim was carrying when he was attacked in a crowded airport terminal.

“We have established that Kim Chol is Kim Jong Nam,” Malaysian national police chief Khalid Abu Bakar said.

“We have fulfilled the requirements of the laws on his identification.”

He refused to say how police identified Kim, saying “the safety and security of the witnesses” are at stake.

Malaysian authorities have asked for Kim’s immediate family to provide DNA samples to identify the body, but no-one has come forward. Malaysia’s prime minister has said they may be too scared to do so.

Khalid said Kim’s relatives have been notified, but have not claimed the body.

Malaysia’s investigation into the killing has infuriated North Korea.

Although Malaysia has never directly accused North Korea of being behind the attack, many speculate that it must have orchestrated it.

Experts say the VX nerve agent used to kill Kim was almost certainly produced in a sophisticated state weapons laboratory, and North Korea is widely believed to possess large quantities of chemical weapons.

Malaysian authorities said the two women who allegedly poisoned Kim were recruited by a team of North Koreans. North Korea has denied any responsibility and accused Malaysia of being swayed by the North’s enemies.

Relations have steadily deteriorated, with each country expelling the other’s ambassador. On Tuesday, North Korea announced that it was blocking all Malaysians from leaving the country until a “fair settlement” of the case was reached. Malaysia then barred North Koreans from leaving its soil.

Four of the seven North Korean suspects being sought by Malaysia are believed to have left the country the day Kim was killed. Police say the remaining three suspects, including a North Korean diplomat, are believed to be in hiding at the North Korean Embassy in Kuala Lumpur.

The attack was caught on surveillance video which shows two women approaching Kim and apparently smearing something on his face. He was dead within 20 minutes, authorities say. Two women – one Indonesian, one Vietnamese – have been charged with murder but say they were duped into thinking they were playing a harmless prank.