Story highlights U.N agency, human rights groups rally to the cause of woman awaiting execution

They say she was a victim of sexual assault and killed her attacker in self-defense in 2007

The man who was killed was a member of Iran's Intelligence Ministry

Under Iran's Islamic law, the family of the slain man could agree to stay the execution

The United Nations and international human rights groups joined a growing call on Monday urging the Iranian government to call off the impending execution of a 26-year-old woman convicted of murder.

Reyhaneh Jabbari was sentenced to death for the 2007 killing of Morteza Abdolali Sarbandi, a former employee of Iran's Ministry of Intelligence and Security.

The Office of the High Commissioner for Human Rights alleges the killing was an act of self-defense against a rapist and says Jabbari never received a fair trial.

In a statement on Monday, the U.N. Office said testimony from "reliable sources" indicates Sarbandi hired Jabbari -- then a 19-year old interior designer -- to work on his office. Jabbari stabbed Sarbandi after he sexually assaulted her, the statement said.

The United Nations and several international rights groups say Jabbari's conviction was based on a false confession obtained under intense pressure and threats from Iranian investigators.

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"The Iranian authorities should review her case and refer it back to court for a retrial, ensuring that the defendant due process rights guaranteed under both Iranian law and international law," said Ahmed Shaheed, the U.N. special rapporteur on the situation of human rights in Iran.

In a statement on Sunday, Amnesty International said, "Sarbandi's association with the Ministry of Intelligence may have affected the impartiality of the court's investigation."

International calls to halt the execution grew louder on Monday after several reports came out that Jabbari would be executed on Tuesday. However, both Jabbari's lawyer and the spokesman for Iran's judiciary dismissed the reports, saying no date for the execution had been set.

The judiciary also held out the possibility that the family of Sarbandi would forgive the killer and agree to stay the execution, an option available under Iran's Islamic penal code.

"There was a lot of this type of guessing that suggested that the sentence may not be carried out if the people (next of kin of the man killed) agreed," said Judiciary spokesman Gholam-Hossein Mohseni-Ejei, according to semi-official Mehr News Agency.

"There is still time until the date of execution of the sentence and the plaintiffs may at the last moment agree to clemency."

Iranian Oscar winner Asghar Farhadi has joined scores of Iranian artists and musicians in calling for a halt to the execution. In an open letter, Farhadi asked the victim's family to pardon Jabbari.

"If you pardon her, I will call that day the Day of Pardon," Farhadi wrote in his letter.

Rights groups have criticized the Islamic Republic of Iran for a surge in executions under Hassan Rouhani, in his first year as President.

According to the United Nations, Iran has executed at least 170 people this year. In 2013, Iran executed more people than any other country with the exception of China, the world's most populous nation. Iran, with almost 81 million people, is ranked 19th.