BUENOS AIRES • A 92-year-old activist in Argentina who has spent decades searching for a granddaughter abducted during the country's 1976-83 military dictatorship plans to resume her search - after having been misinformed that the woman had been found.

Ms Maria "Chicha" Mariani was a founder of the Grandmothers of the Plaza de Mayo, a group that fought to find children stolen or illegally adopted during Argentina's so-called Dirty War.

She is one of the country's best-known rights activists, and the Christmas Eve news that she had finally found her granddaughter - who was abducted as an infant when regime agents killed the mother - was the feel-good story of the season.

President Mauricio Macri even congratulated her on Twitter.

Then, on Friday, the government said two genetic tests showed that the 39-year-old woman in question was not Ms Mariani's granddaughter after all.

Ms Mariani, who is nearly blind, "is extremely sad, and in pain", spokesman Juan Martin Padilla said on Saturday.

Apparently, "she let herself get swept up in the emotion when someone came up to her with a test result that showed positive", Mr Padilla said.

That DNA test was carried out privately.

Despite the crippling disappointment, Ms Mariani has not given up, Mr Padilla said.

"We are going to keep working as we always have, to see justice done, the truth told, and no one forgotten," he told reporters outside the activist's home.

An estimated 500 babies were stolen by Argentina's military regime, which abducted, tortured and killed opponents and suspected sympathisers.

Some 30,000 people were killed or "disappeared" during the dictatorship.

AGENCE FRANCE-PRESSE