"The exact number will never be known, but it certainly is less than 1,000 dead," said Otilia de Koster of the human rights center.

Last fall, the police said, a man came to his office and told him to close the human rights center at Mustansiriyah University.

She returned home in April, formally separating herself from the human rights center but continuing to pursue high-profile political cases.

The workers' rights center is the second created by Neighborhood Legal Services.

The human rights center said the report was based on "credible firsthand information from a variety of unrelated sources."

Most of those killed, the human rights center said, were peasants and leftists, including students and union organizers.

The threatening note was directed at the rights center: "If you continue with others, it will cost you."

They have barred travel abroad for political conferences and shut down a human rights center financed by the European Union.

The existence of its human rights centre created the impression that things were not that bad in Iran.