Malaysian authorities are decontaminating the airport where the estranged half-brother of North Korean ruler Kim Jong Un was killed with a deadly nerve agent 11 days ago.
Meanwhile police said one of the women suspected of attacking Kim Jong Nam had been ill since the attack.
Police did not initially decontaminate the Kuala Lumpur airport where Mr Kim was attacked on February 13, but in a text message to a reporter, national police chief Khalid Abu Bakar said: "We are doing it now."
The move came after authorities said banned chemical weapon VX was used to kill Mr Kim.
Mr Khalid said one of the two women accused of wiping the toxin on Mr Kim's face was later ill and suffered from vomiting.
He did not say which of the women - one Indonesian and one Vietnamese - had fallen ill.
VX was detected on Mr Kim's eyes and face, Mr Khalid said, citing a preliminary analysis from Malaysia's Chemistry Department.
The death of Mr Kim, whose daylight assassination in a crowded airport terminal seems straight out of a spy novel, has unleashed a diplomatic crisis that escalates by the day.
A Japanese religious cult that carried out the nerve gas attack on Tokyo's underground rail network in 1995 also used VX.
The Aum Shinrikyo cult, which killed about a dozen commuters and severely injured dozens more with sarin, another kind of nerve gas, tried VX out on at least three victims, killing one whom cult members believed was a police informant.
In their trial, the cultists said they practised using syringes to spray the deadly chemical on people's necks as they pretended to be out jogging.
The suspected informant spent 10 days in a coma before dying.
With each new twist in the Kim case, international speculation grows that Pyongyang dispatched a hit squad to Malaysia to kill Kim Jong Un's exiled older sibling while he was checking in for a flight to Macau, where he lived with his family.
North Korea has condemned Malaysia's investigation as full of "holes and contradictions" and accused authorities of being in league with Pyongyang's enemies.
After the attack, Mr Kim sought help from airport staff but fell into convulsions and died on the way to hospital within two hours, police said.
The case has perplexed toxicologists, who question how the women could have walked away unscathed after handling a powerful poison, even if, as Malaysian police say, the women were instructed to wash their hands right after the attack.
Dr Bruce Goldberger, a leading toxicologist who heads the forensic medicine division at the University of Florida, said even a tiny amount of the nerve agent - equal to a few grains of salt - was capable of killing.
It can be administered through the skin and there is an antidote that can be administered by injection.
US medics and military personnel carried kits with them on the battlefield during the Iraq war in case they were exposed to the chemical weapon.
"It's a very toxic nerve agent. Very, very toxic," Dr Goldberger said.
He said symptoms from VX would generally occur within seconds or minutes and could last for hours starting with confusion, possible drowsiness, headache, nausea, vomiting, runny nose and watery eyes.
Before death, there would probably be convulsions, seizures, loss of consciousness and paralysis.
The case has marked a serious turnaround in relations between Malaysia and North Korea.
While Malaysia is not one of Pyongyang's key diplomatic partners, it is one of the few places in the world where North Koreans can travel without a visa.
As a result, for years, it has been a quiet destination for Northerners looking for jobs, schools and business deals.
Malaysia has three people in custody, including the two suspected attackers.
Authorities are also seeking several other people, including the second secretary of North Korea's embassy in Kuala Lumpur and an employee of North Korea's state-owned airline, Air Koryo.