A Japanese 'black widow' faces being hanged for murdering three boyfriends she met online.

Kanae Kijima, 42, killed the men through carbon monoxide poisoning by burning charcoal briquettes after giving them sleeping tablets.

She met them online and dated them for their money before killing each in the space of eight months, the Daily Mail reported.

Kijima, who has married twice since she was detained in 2009, faces execution after Japan's Supreme Court on Friday dismissed her final appeal.

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Her legal team has claimed her innocence, saying the three men were likely to have committed suicide.

The death penalty has overwhelming public support in Japan, despite repeated protests from European governments and human rights groups.

Executions are by hanging but it can take years before they are carried out.

The case has been closely followed in Japan and major media flashed news of the top court decision across television screens.

Kijima writes a blog from the detention centre where she has been held, detailing her life inside, the food and talking about men she likes.

In the latest post on Thursday, she wrote to her readers: "I hope to see you again somewhere someday."

Kijima's first victim, 53-year-old Takao Terada was found dead in Tokyo in January 2009.

Kenzo Ando, 80, died in his home in Chiba prefecture in May 2009, and three months later 41-year-old Yoshiyuki Oide was found poisoned in a rented car, also from briquette fumes.

Kijima was convicted without the witness testimony or confession often relied upon in Japanese prosecutions.

Instead prosecutors rested their case on layers of circumstantial evidence, such as Kijima's purchases of sleeping pills and coal briquettes, in addition to the fact that she had met with each man shortly before he died.

She was also found guilty of seven other lesser crimes, including fraud and theft.