A woman who poisoned her elderly lovers with cyanide and then pocketed millions from their insurance payouts was convicted of their murders by a court in Japan on Tuesday.

The Kyoto District Court sentenced 70-year-old Chisako Kakehi to hang to death for killing her husband and two other former partners as well as attempting to murder a fourth man between 2007 and 2013.

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"In all four cases, the accused made the victims drink cyanide with intent to kill," Judge Ayako Nakagawa told the court, Japanese broadcaster NHK reported.

"The cases were well prepared in advance. They were cunning and malicious. I have no choice but to impose the ultimate penalty," the judge added.

The court rejected arguments from defense lawyers that Kakehi was not criminally liable because she was suffering from dementia.

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'Black Widow'

Dubbed the "Black Widow" or "The Poison Lady," Kakehi was arrested in November 2014 over the death of her 75-year-old husband a month after they had married. The other men she is convicted of killing were former boyfriends aged 71 and 75. She attempted killing a fourth man, aged 79.

The court said the defendant encouraged the victims to take cyanide capsules, saying they were health supplements. She obtained the poison while running a printing plant and investigators discovered a small packet of the poison buried in a flower pot.

Kakehi was reportedly married at least three times and had three other partners who died within a few years of starting relationships with her. She also amassed around 1 billion yen ($8.8 million; €7.6 million) in inheritances over 10 years after she was made the beneficiary of her partners' life insurance policies.

She subsequently lost most of her fortune through unsuccessful financial trading.

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Kakehi initially refused to speak when her trial began in June, but she later admitted to killing her husband over alleged unfair financial treatment.

"I killed him ... because he gave other women tens of millions of yen but did not give me even a penny," she told the court, according to Jiji Press.

She had earlier told judges she was ready to face the gallows.

"Even if I were executed tomorrow, I would die smiling," Kakehi previously told the judges.

Her lawyers immediately appealed Tuesday's ruling to a higher court, suggesting the trial could continue for years.

rs/rc (AP, AFP, dpa)