(CNN) The chemical substance used to kill Kim Jong Nam was a VX nerve agent , an internationally-banned chemical weapon that can kill within minutes, according to a preliminary report by the Chemistry Department of Malaysia.

Malaysian police said in a statement Friday that tests on Kim's eyes and face revealed the presence of the substance.

Nerve agents are the most toxic and fast-acting substance known in chemical warfare -- and VX is the most potent of all of them, according to the US Centers for Disease Control and Prevention (CDC).

Kim, the estranged half-brother of North Korean leader Kim Jong Un, died on February 13 before he was scheduled to board a flight from Kuala Lumpur to Macau.

North Korea rejects that version of events, saying that the women would be dead if they had put a lethal chemical on their hands. It vehemently denies any involvement in Kim's death.

There are binary versions of chemical weapons, including VX, which aren't lethal until two compounds are mixed, according to the Organisation for the Prohibition of Chemical Weapons (OPCW).

Binary systems are usually employed for the safe storage of chemical weapons.

How it works

VX inhibits the operation of an enzyme that helps the body's nervous system function, causing paralysis and suffocation.

"VX is probably the state-of-the-art nerve agent," CNN military analyst Rick Francona said. "It is probably the most lethal of all the nerve agents ever designed."

Symptoms can appear after a few seconds, and even small doses -- as little as 10 mg on the skin -- can affect people. Larger exposure can lead to convulsions, paralysis and deadly respiratory failure.

VX is most dangerous when inhaled, rather than absorbed through the skin, according to Nial Wheate, a chemical weapons health expert at the University of Sydney.

"It's not (meant as) a skin agent. It's a thing that you aerosol through the air," he said.

The nerve agent is listed in the top tier of deadly substances in the Chemical Weapons Convention , which North Korea has not signed.

Despite its lethality, it's not particularly difficult to make, Francona and other experts say.

Pyongyang has had the capability to produce and use nerve agents for some time. A 2009 report from the International Crisis group estimated that the country possessed 2,500 to 5,000 tons of chemical weapons at the time, which could be delivered using artillery, rocket launchers and ballistic missiles, among other weapons.

But the blast from a delivery system like missile would likely destroy much of the VX, said Wheate. It's more meant for aerosol use in close quarters.

"There's no one weaponizing this stuff, this is old school," he said.

JUST WATCHED Video appears to show Kim Jong Nam attacked Replay More Videos ... MUST WATCH Video appears to show Kim Jong Nam attacked 01:28

The suspects

Malaysia authorities have named 11 people in connection with their investigation, though not all are considered suspects.

Three are currently in custody. One is a North Korean man, and two are the women who police believe wiped Kim's face: Siti Aishah of Indonesia and Doan Thi Huong of Vietnam.

Indonesian police said last week that Aishah believed she was participating in a prank for a TV show , but that was adamantly shot down by Bakar at his Wednesday news conference.

"These two ladies were trained to swab the deceased's face," he said. "They knew it was toxic."

Denials and diplomatic fallout

Diplomatic ties between North Korea and Malaysia are growing increasingly frayed over the investigation.

North Korea has accused Malaysia of being unduly influenced by South Korea's early claim that Kim was poisoned by the North.

Pyongyang's ambassador to Malaysia, Kang Chol, accused his host country of conspiring with "hostile forces," prompting the Malaysian Prime Minister to recall his ambassador to North Korea and summon Kang.

An article published in North Korean state media Thursday fiercely rebuked Malaysia for its continued refusal to hand over Kim's body without DNA from a next of kin.

"This proves that the Malaysian side is going to politicize the transfer of the body in utter disregard of international law and morality and thus attain a sinister purpose," Thursday's article said.

Bakar, the Malaysian police inspector-general, accused North Korea of impeding the investigation.

He said Wednesday that the North Koreans had neither responded to requests to hand over the four suspects in Pyongyang, nor had they helped police find three North Koreans believed to be in Malaysia -- including an embassy employee -- who are wanted for questioning.

If the three who police think are still in Malaysia do not come forward, they will seek arrest warrants, Bakar said.