The president of the Ivory Coast has pardoned 800 people including the former first lady Simone Gbagbo, who was serving a 20-year sentence for her role in the deadly post-election violence of 2010.

Gbagbo was convicted of undermining state security, disturbing public order and organising armed gangs when her husband, Laurent Gbagbo, refused to accept the election result and leave the presidential palace.

The man who won that election, Alassane Ouattara, announced he would free her and hundreds of others in the interests of “peace and true reconciliation”.

“On Monday I signed an amnesty order that will benefit about 800 citizens prosecuted or sentenced for offences related to the post-election crisis of 2010, or state security offences committed after May 21, 2011,” the president said, adding that 500 of them had already been released, but would have their criminal records erased. The other 300 would be released soon, he said.

Gbagbo was also tried for crimes against humanity and war crimes, but was acquitted last March. Although the international criminal court (ICC) issued an arrest warrant against her, Ivorian authorities refused to hand her over, and her trial in Abidjan was boycotted by victims’ groups who said there were doubts about its credibility. Human rights groups criticised her acquittal, saying serious questions about her alleged role in brutal crimes had gone unanswered, showing how important the ICC case against her was.

The former ministers Moise Lida Kouassi and Assoa Adou, and Kamagaté Souleymane, who was a rebel when Laurent Gbagbo was in power, will also be freed under the amnesty, which appeared to be an effort to assuage political tension ahead of the 2020 election. Ouattara recently said he was free to run again in that poll despite having already served two terms, as the constitution had been changed.

“This is an act of mercy from the whole nation towards her sons and daughters,” the president said. “I invite all those who benefit from this amnesty to ensure that our country never again has to go through events like those and never again sinks into violence.”

Gbagbo was delighted, her lawyer told the magazine Jeune Afrique, and expected to be released later this week.

Laurent Gbagbo refused to concede the presidential election to Ouattara in November 2010, setting off four months of fighting in which 3,000 people died. He was finally ejected from his bunker at the presidential palace in April 2011 and was paraded wearing a Hawaiian shirt and a hurt expression, alongside his wife, in a bedroom of Abidjan’s Hotel du Golf.

He is on trial at the ICC in The Hague for crimes against humanity including murder, rape and persecution. The prosecution rested its case against him in January after calling 82 witnesses; the defence has not yet started its case, but Gbagbo’s lawyer has urged the court to dismiss the case and release him. The next court hearing will be on 1 October.