Sakineh Mohammadi Ashtiani told an interviewer that she was an accomplice to the killing of her husband and that she had a relationship with her husband's cousin.
Her lawyers say she was tortured into making the TV confession.
Ashtiani spoke shakily in her native Azeri when she appeared on Iranian state television to make her purported confession.
She told an interviewer through a voiceover that she had been involved in the death of her husband and that she had had an affair with her husband's cousin.
WATCH: You can see the state television broadcast here, with Ashtiani appearing from around the 10:30 mark.
She said she was aware that the cousin had said he would kill her husband, and had given her details of how he planned to do it. But she said she thought the threat was a "joke" that she did not take seriously at the time.
The television then broadcast the prosecutor of Iran's East Azerbaijan Province, Malek Ajdar Sharifi, saying: "The deceased was given an injection to fall asleep by his wife. Then the man arrived and put him into the bath and put two electrical lines on his body and killed the deceased."
Lawyers for the woman vehemently reject the confession, saying it was extracted by torture. One of the lawyers, Houtan Kian, told the British daily "The Guardian" that Ashtiani was severely beaten and tortured over two days to make her appear on television.
Another lawyer, Mohammad Mostafaei, said the program on which she appeared, called "20:30," is controlled by the intelligence services in Iran. He was speaking to CNN from Norway, where he has sought asylum after fleeing Iran in July, fearing arrest.
In her interview, Ashtiani denied ever having met Mostafaei and asked how he dare spread lies about her. Mostafaei, however, told CNN that he had met her in prison in Tabriz last year and that he was her legal counsel.
Ashtiani has already been flogged 99 times after being found guilty of adultery in the same case in 2006. The case was later reopened after a court in Tabriz suspected her of murdering her husband. Despite being acquitted, the adultery charge was reviewed and a stoning sentence imposed based on the "judge's knowledge."
Ashtiani's case captured overseas attention after it was reported this summer that the 43-year-old mother's execution by stoning was imminent. The Iranian authorities subsequently reviewed the case and reportedly changed the sentence to that of hanging.
U.S. Secretary of State Hillary Clinton said on August 10 that the United States was "troubled" by the case of Ashtiani, whose fate is "unclear." She said the case had not "proceeded with the transparency or due process enshrined in Iran's own constitution." And she noted the lawyer representing her "felt that he had to flee Iran."
A human rights campaign group, the International Committee Against Stoning, called the television show "toxic propaganda."
Hassiba Hadj Sahraoui, the deputy director of Amnesty International's Middle East and North Africa program, said that "it appears that Iran's authorities have orchestrated this 'confession,' following the call for a judicial review and now appear to be inventing new charges of murdering her husband."
The British Foreign Office said it was appalled by the televised confession and called on Iran "to comply with the international human rights obligations they have independently signed up to."
Meanwhile, Brazil has again urged Iran to make a humanitarian gesture over Ashtiani. Foreign Minister Celso Amorim said that would be good for Iran's image. Brazil's President Luiz Ignacio Lula da Silva has offered her asylum in his country.
written by Breffni O'Rouke based on RFE/RL and agency reports