French serial killer Charles Sobhraj, responsible for multiple murders of young foreigners in the 1970s across Asia, was freed from a Nepali jail on Friday, an AFP reporter said.

Sobhraj, 78, whose life was chronicled in the successful series "The Serpent", was to be transferred to immigration detention ahead of his scheduled deportation to France, police said.

Nepal's top court ruled on Wednesday that the expulsion should happen within 15 days but his lawyer had suggested on Thursday that this might be delayed because of health issues.

"Once he is taken to the immigration, then it will be decided what would be the next course. He has a heart issue, so he wants to get treatment from the Gangalal hospital," Gopal Shiwakoti Chintan told reporters.

The court ordered Sobhraj, who had heart surgery in 2017, should be released on health grounds after serving more than three-quarters of his sentence for murdering two North Americans in Nepal in the 1970s.

A French foreign affairs ministry spokesman told AFP on Thursday that its embassy in Nepal was monitoring the situation.

"If a request for expulsion is notified to them, France would be required to grant it since Mr. Sobhraj is a French national."

'Bikini killer'

Born in Saigon to an Indian father and a Vietnamese mother who later married a Frenchman, Sobhraj embarked on an international life of crime and ended up in Thailand in 1975.

Posing as a gem trader, he would befriend his victims, many of them Western backpackers on the 1970s hippie trail, before drugging, robbing, and murdering them.

Suave and sophisticated, he was implicated in his first murder, a young American woman whose body was found on a beach wearing a bikini, in 1975.

Nicknamed the "bikini killer", he was eventually linked to more than 20 murders.

He was arrested in India in 1976 and ultimately spent 21 years in jail there, with a brief break in 1986 when he drugged prison guards and escaped. He was recaptured in the Indian coastal state of Goa.

Released in 1997, Sobhraj lived in Paris, giving paid interviews to journalists, but went back to Nepal in 2003.

He was then dramatically spotted in a casino playing baccarat by journalist Joseph Nathan, one of the founders of the Himalayan Times newspaper, and arrested.

"He looked harmless… It was sheer luck that I recognized him," Nathan told AFP on Thursday. "I think it was karma."

A court in Nepal handed him a life sentence the following year for killing US tourist Connie Jo Bronzich in 1975. A decade later he was also found guilty of killing Bronzich's Canadian companion.

Behind bars, Sobhraj maintained that he was innocent of both murders and claimed he had never been to Nepal before the trip that resulted in his arrest.

"I really didn't do it, and I think I will be out," he told AFP in 2007 during an interview at Kathmandu's Central Jail.

Thai police officer Sompol Suthimai, whose work with Interpol was instrumental in securing the 1976 arrest, had pushed for him to be extradited to Thailand and tried for murders there.

But on Thursday, he told AFP that he did not object to the release, as both he and the criminal he once pursued were now too old.

"I don't have any feelings towards him now that it's been so long," said Suthimai, 90. "I think he has already paid for his actions."