Seth Mydans, Jakarta – Human rights workers who are investigating scores of organized gang rapes during three days of rioting here in May say they and the victims have been receiving threats from unidentified men.

In interviews, the investigators said they had confirmed the rapes of 168 women during the riots, of whom 20 had died during or after the assaults. They said they presumed that many other women had either fled the city or were too traumatized to report their rapes.

Some victims have been cowed into silence by threats or by rumors of another round of attacks and rapes, the investigators said. Others have committed suicide. And they said they had heard reports of additional rapes and sexual assaults in the weeks after the riots.

Most of the attacks, like most of the looting and arson, were directed against the ethnic Chinese minority, which often becomes a scapegoat in times of conflict or hardship in Indonesia.

The human rights workers said their continuing investigation had reinforced their belief that the rapes, some of them involving girls as young as 9, had been organized and coordinated in the same way as much of the looting and arson.

A growing body of reports from witnesses has confirmed that many of the attacks on property and residents, including the rapes, were instigated or carried out by organized groups of up to a dozen men. These groups traveled the city in vehicles, inciting crowds to violence, according to reports released by the Government's National Commission for Human Rights and the Jakarta Social Instititute, a private Catholic charity that is investigating the riots.

Suspicion has fallen on the military or other security forces, particularly after the military acknowledged last week that members of its special forces had been involved in kidnappings of opposition activists in the weeks before the riots.

The threats against workers at women's crisis centers and against some victims who have called the centers' hot lines also indicate the involvement of people able to monitor their activities and listen to their telephone conversations, said Ita F. Nadia, an organizer of Volunteers for Humanity, a private aid group. "We have received telephone calls and anonymous letters terrorizing our workers," she said. "They say they will rape the females and castrate the males."

The Rev. Sandyawan Sumardi, who heads the private Jakarta Social Institute, said he had also received threats. In addition, he said, threats have been made against witnesses, family members and hospital workers who treated the victims.

Photographs purporting to show the victims of the rapes have been circulating, some of them on the Internet. Ms. Ita said she believed that these were not in fact photographs of riot victims and that they were intended to sow fear. Because of fears that security forces were involved, victims have avoided reporting the rapes to the police, said Kamala Chandrakirana, a spokeswoman for Ms. Ita's group, which now employs as many as 300 volunteers.

At first the Government seemed to doubt the growing reports of rapes, but after meeting with 25 representatives of women's groups earlier this month, President B. J. Habibie set up a Government task force to study their reports and issued a statement condemning "this inhuman episode in the history of our nation."

He selected his wife, Dr. Hasri Ainun Besari, who is a physician, to be an adviser to the task force. "At first he was saying, 'I don't want this case to be blown up and give a bad name to the Indonesian people,' " Ms. Kamala said. "He was not clear on it at first. He was rambling about how bad the economy was going to be unless he saved it."

But as he heard the women out, Ms. Kamala said, his face took on a look of shock and he asked them to draft a statement for him on his office computer. "On behalf of the Government and the nation, I condemn the simultaneous acts of violence during the riots, including the violence perpetrated against women," the statement read.