Claiming there is "no justice" in Iran, a 22-year-old man has sent a letter to the Islamic Republic's top officials in a last-ditch effort to save his mother from being stoned to death for adultery.

Sakineh Mohammadi Ashtiani, 42, was convicted in 2006 and has already spent five years in prison and endured 99 lashes for her illicit relationship with two men. Now, to complete her sentence, she will be put to death by stoning, an execution that appears to be imminent.

Ashtiani's son, Sajad Ghadarzade, has petitioned Iran's Supreme Leader, Ayatollah Ali Khamenei, its president, Mahmoud Ahmadinejad and its judiciary chief, Ayatollah Sadeq Larijani, to protest his mother's impending execution.

"I, as an Iranian citizen who has not succeeded in getting an audience with your office, say to you, the head of the judiciary who tells the television networks day in, day out, that justice must prevail and officials guilty of misconduct must be punished, that there is no justice in this country," Ghadarzade wrote to Larijani.

The young man, who lives in the northern city of Tabriz, wrote that he has traveled at least six times to Tehran to visit the three leaders and has written to them more than a hundred times -- but he has not received a response.

Iran is facing growing criticism for the imminent stoning of the mother of two. Among those who have issued statements condemning the sentence are the U.S. State Department, Senate Foreign Relations Committee Chairman John Kerry and European Union foreign affairs chief Catherine Ashton.

According to a statement released last week by Amnesty International, which tracks death penalty cases worldwide, Ashtiani has retracted a confession she made during interrogation, indicating that the statement was made under duress.

She was convicted by three of five trial judges on the basis of the "knowledge of the judge," a provision in Iranian law that allows judges to rule even in the absence of clear or conclusive evidence. Her death sentence was confirmed by Iran's Supreme Court in May 2007, according to the statement.

Under Iranian law, Ashtiani will be buried up to her chest, and people will throw stones at her until she dies. (Men are buried up to their waist prior to stoning.)

"If the execution goes ahead, that's what would happen to her," said Ann Harris, a London-based Iran researcher for Amnesty International.

She said a date for Ashtiani's execution has not yet been set, but it could occur at any time since there is no legal obstacle to stop it.

"She's been on death row for some time now," Harris said. "It could be at short notice. Without pressure on her case, she remains at risk."

At least 139 executions have taken place in Iran this year through Wednesday, Harris said, adding that 10 others -- including three women -- are facing execution by stoning.

U.S. State Department officials did not return several messages seeking comment, but a spokesman said Thursday that the agency has "grave concerns" that Ashtiani's punishment does not fit her crime and cited "significant" human rights concerns.

Kerry, D-Mass., blasted the execution method as "appalling" and "barbaric" and called for the government of Iran to abolish it as a form of capital punishment.

Attempts to reach Ashtiani's attorney, Mohammad Mostafaei, were not successful Thursday.

FoxNews.com's Joshua Rhett Miller and Newscore contributed to this report.