HARARE, Zimbabwe - President Robert Mugabe's regime has renewed assaults on dissidents, a human-rights group said yesterday, even as he faced more international pressure to step down amid a cholera outbreak that has killed nearly 600 people.

Brian Raftopoulos, organizer of the Solidarity Peace Trust, said a number of activists had been abducted and protests violently quashed by riot police.

"As long as the [political] stalemate continues, we will see an increasing crackdown," Raftopoulos told reporters in South Africa. "The Mugabe regime is presiding over the death of the nation of Zimbabwe."

Mugabe's neighbors and others have renewed calls on him to surrender power, not just share it with his opposition as envisioned in a unity-government deal that has been stalled since September.

Mugabe's aides responded to the calls, which are similar to denunciations he has resisted for years, by accusing the West of trying to use the cholera crisis as an excuse to topple the government.

Zimbabwe Information Minister Sikhanyiso Ndlovu told reporters that "the cholera issue has been used to drive a wedge among us," that the deaths were caused by Western sanctions, and that the disease was "under control."

He dismissed world leaders, including President Bush, former U.S. President Jimmy Carter, and prime ministers Raila Odinga of Kenya and Gordon Brown of Britain, who have asked that Mugabe step down. "I don't want to hear their dirty mouths," he said.

Yesterday, the United Nations raised the cholera toll to 589 dead out of 13,960 cases.

Zimbabwe was cooperating with international aid agencies fighting the epidemic, and last week declared a health emergency because of cholera and the collapse of its health services.

Peter Lundberg, the international Red Cross representative in Zimbabwe, said nations and agencies were ready to respond to a "critical humanitarian need."

He said the Red Cross had exhausted initial cholera treatment and water-purification supplies and was preparing an appeal for more donations and cash.

He was concerned that coming rains would further spread cholera in a population weakened by hunger. He noted Zimbabwe's neighbors were being affected.

South Africa has been caring for scores of Zimbabwean cholera victims who have crossed the border seeking help.

The U.N. health organization said yesterday that 468 cholera cases had been detected in South Africa, with nine deaths, and that Zimbabwe's epidemic also had spread to Mozambique and Botswana.

WHO spokeswoman Fadela Chaib said the cases in South Africa were probably a mix of cholera already found in South Africa and spillover from Zimbabwe.