An Ivory Coast court has found former First Lady Simone Gbagbo not guilty of war crimes and crimes against humanity after a trial on her alleged role in post-election abuses that led to the deaths of thousands.

Judge Kouadio Bouatchi, with the country's highest criminal court, said a jury unanimously voted on Tuesday to free Gbagbo.

The prosecution had asked for a life sentence, saying she participated on a committee that organised attacks against supporters of her husband's opponent after the 2010 election.

Once dubbed Ivory Coast's "Iron Lady", Gbagbo, who was not in court on Tuesday, must still serve 20 years in prison after being found guilty in 2015 of offences against the state.

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The prosecution had called on the jury to find the 67-year-old wife of ex-president Laurent Gbagbo "guilty of crimes against humanity and war crimes and sentence her to life imprisonment," said prosecutor Aly Yeo.

"After her spouse came to power, she started to impose herself as the real head of Ivory Coast, the army, the police and gendarmerie," Yeo said.

Trial criticised

Laurent Gbagbo is on trial for crimes against humanity, including murder, rape and persecution, having been handed over in November 2011 to the International Criminal Court (ICC) in The Hague.

The ICC also wanted to prosecute his wife and issued a warrant for her arrest, but Ivorian authorities refused to hand her over, insisting she would receive a fair trial at home.

Ivory Coast descended into civil war in 2011 after Gbagbo's refusal to accept defeat to Alassane Ouattara in a presidential runoff election. About 3,000 people were killed in the conflict.

"We regret this decision when we think of the many victims," Soungaola Coulibaly, lawyer for the victims, told Reuters.

"If Simone Gbagbo is declared not guilty of these acts then who was? ... The victims do not understand this decision."

Human Rights Watch said the judgment left "unanswered serious questions about her alleged role in brutal crimes".

"The acquittal ... reflects the many irregularities in the process against her," Param-Preet Singh, associate director in Human Rights Watch's International Justice programme, said.

"The poor quality of the investigation and weak evidence presented in her trial underscore the importance of the ICC's outstanding case against her for similar crimes."