Princess Ashraf Pahlavi, the twin sister of Iran's last shah, who has died at the age of 96, was a trailblazer for women's rights who lived an opulent life that was never far from controversy.

Born in Tehran, she was considered a powerful force behind her brother and a sometimes fierce critic of him in private, playing an important role in domestic and international politics.

An official with the office of the shah's son, her nephew Reza Pahlavi, told AFP the princess died in Monte Carlo on Wednesday, noting that she had long suffered from Alzheimer's disease.

Iranian media confirmed the death, with several outlets posting unflattering accounts of her private life alongside details of official posts she held under her brother's rule.

The Islamic revolution of 1979 that toppled Shah Mohammad Reza Pahlavi transformed Iran and meant the princess never returned, a fact she had reflected on in her final days, her nephew said.

"She was thinking about Iran till the very last moments of her life, and she passed away with hopes for her homeland’s liberation," wrote Reza Pahlavi in a Facebook tribute.

"May her soul find joy and the memory of her kind image last forever," he said, noting her efforts for women's rights, social welfare and campaigns for literacy in Iran and abroad.

"With a heart full of affection for her country, she made outstanding efforts," added Pahlavi, who lives near Washington.

Three-times married, the princess is survived by a son, Prince Shahram, five grandchildren and several great grandchildren.

From exile she supported cultural, literary and artistic heritage projects that aimed to restore what she saw as their near desecration by Iran's revolutionary rulers.

In the royal era, the princess was regarded as a talented diplomat, leading Iran's delegation to the United Nations General Assembly for more than a decade.

On Saturday, IRNA, Iran's official news agency, said she headed the country's human rights committee, was chief of the Women's Organisation of Iran and its representative to the UN human rights commission.

- Privilege, and tragedy -

The princess basked in her privilege and wealth, often pictured at the gaming tables of European casinos, but experienced family tragedy and survived an assassination attempt.

Shahriar Shafiq, her son from a second marriage was gunned down in front of the princess's home in Paris in 1979, an assassination blamed on the new regime in Tehran.

Two years earlier, she walked away unhurt after her lady-in-waiting was killed and her driver wounded when gunmen fired on her Rolls-Royce as she left a casino in Cannes.

In “Faces in a Mirror: Memoirs from Exile”, she revealed an unhappy childhood, saying she was overlooked. Instead, she said her sister, Princess Shams, was more cherished by her parents and her brother was coveted, as he was destined for the throne.

In the book, published in 1980, she described herself as a rebel with a quick temper.

Vatan-e-Emrooz, a conservative daily in Iran, noted Saturday that the princess died exactly 80 years to the day after her father, Shah Reza Pahlavi, banned women in Muslim Iran from wearing the veil.

In a sign of the religious and political change, the wearing of at least a headscarf and loose clothing by women to cover their bodies was made mandatory after the revolution.

Princess Ashraf was considered a powerful spokeswoman and ally for her brother, leading to her forever being loathed by Iran's religious rulers.

"In the Pahlavi era, there was no woman as influential in foreign and domestic policy as Ashraf. She played a major role in the coup," Fars News Agency reported Saturday, referring to the 1953 overthrow of the country's democratically elected nationalist Prime Minister Mohammad Mossadegh.

The agency, affiliated with Iran's powerful Revolutionary Guards, said the US- and British-orchestrated coup that brought the princess's brother to power led to Ashraf’s "interference" in international affairs.

"She went on numerous foreign trips on behalf of her brother and negotiated with governments hostile to Iran," it said.

Stephen Kinzer, author of "All the Shah's Men", a book about the revolution, said of the princess: "Ashraf's tongue-lashings of her brother were legendary, including one in the presence of foreign diplomats where she demanded that he prove he was a man or be revealed to all as a mouse."