JAKARTA, Oct 1 (Reuters) - A 21-year-old Indonesian man from West Jakarta has died of bird flu, taking the death toll from the virus to 86, a health ministry official said on Monday.

Experts are still investigating how the man contracted the virus, which is most commonly spread to humans through contact with sick fowl, Tini Suryanti, spokesman of the Jakarta health office, told Reuters.

"We don't know how he could have come in contact with sick chicken, since backyard poultry has long been banned by the city government," Suryanti said.

The victim, who died in hospital on Sunday, fell ill on Sept. 18 but was only hospitalised a week later, the bird flu centre's Joko Suyono told Reuters.

"He was brought too late to the hospital. He was already suffering from pneumonia, and three days later he died," Suyono said.

Bird flu is endemic in bird populations in nearly all parts of Indonesia, where millions of backyard chicken live in close proximity to people.

The Jakarta government banned backyard poultry in February in a bid to stem a new flare-up in bird flu after four people died in the beginning of the year in the capital.

Indonesia has had 107 confirmed cases from bird flu, of which 86 have been fatal, the highest for any country in the world.