South Korean actor Lee Sun-Kyun, best known for his role in the Oscar-winning film Parasite, has been found dead, authorities have confirmed to the BBC.

The actor, 48, was found unconscious in a car in one of Seoul's main parks on Wednesday.

It is unclear if Lee took his own life, but police said they received a report that he had left home after writing a note.

He had been under investigation for alleged drug use since October.

In Parasite, Lee played the patriarch of the wealthy Park family which is infiltrated by members of a poor family posing as unrelated individuals. The vicious social satire won four Oscars, including best picture.

Yonhap news agency reported that he was suspected of taking drugs such as marijuana and ketamine with a hostess at a bar in Seoul. He had said that though he took what she gave him, he had not known that they were illicit drugs.

The hostess had reportedly told the police that he used drugs at her home multiple times - something he denied. He had earlier requested through his lawyer to take a lie detector test.

His drug tests had returned negative or inconclusive results, the report added.

Police said they regretted that Lee had died in the midst of investigations, but that the inquiry had been "conducted with [his] consent", News1 Korea reported. Lee underwent three rounds of questioning, with one session last Saturday lasting 19 hours, according to Yonhap.

Lee's agency, HODU&U Entertainment, said in a statement: "There is no way to contain the sorrow and despair. We respectfully ask that you refrain from spreading false facts based on speculation... so that [Lee's] final journey will not be unfair."

News of his death sparked strong reactions online.

"I can't imagine how difficult it must have been for him. Rest in peace," read a comment on one of the news reports.

"Aren't celebrities human? People can make mistakes in their lives. It's so sad," another commenter said.

The actor, who was married to actress Jeon Hye-jin and had two young sons with her, had a career spanning more than two decades.

He starred as the lead in dozens of films and TV shows, becoming a household name through the 2010s.

He rose to international fame with Parasite, as it became the first non-English language film to win the Best Picture Oscar.

In South Korea, celebrities are held to high standards of propriety.

Lee had a squeaky-clean, family-man image prior to his alleged drug use, but reports that emerged from the investigation caused considerable damage to his reputation. He was dropped from No Way Out, a mystery TV series that began shooting in October.

According to reports, some businesses were seen taking down posters and advertisements featuring Lee from their stores.

Drug offences, including those involving usage of marijuana, are considered serious crimes in South Korea. Consumption of marijuana carries prison sentences of up to five years.

South Korean President Yoon Suk Yeol has vowed a crackdown on drugs. This year, the country's authorities expanded its drug crimes department and the national police chief promised "a total war" on drug crimes.

Lee is not the only South Korean celebrity who had been investigated for drug use recently. Earlier this month, K-pop star G-Dragon was cleared of drug allegations after weeks of investigations.

Actor Yoo Ah-in is currently standing trial for drug use.