A major HIV drug trial in Cambodia has been shelved amid claims it violated people's human rights.
The trial is set to run in seven other countries
The trial was supposed to be one arm of an international study to see if Tenofovir, which is used to fight HIV, can also protect against the disease.
But sex workers refused to participate unless they were given full medical insurance to protect them against any future illnesses.
Cambodian Prime Minister Hun Sen has now intervened to stop the trial.
Earlier this month, he urged Cambodians to boycott the study, saying the country was not a test bed for "out-of-date" technologies.
He also suggested that the drug should be tested on animals before any human trial was launched.
Cambodian Health Minister Nuth Sokhom said the prime minister was worried the trial would contravene people's human rights.
"He is worried that the drug testing will affect the health of Cambodian people, human values and rights," he said.
The decision was welcomed by the Cambodian Women's Network for Unity, which represents more than 5,000 sex workers.
"We are very happy with this order as we don't want to take part in this drug test. There is no safety guarantee for us," said its director Kao Tha.
"We are so poor that we don't have the money to pay for treatment if we fall sick after the test."
Family Health International, the American organisation, is spearheading the trials and rejects claims that they violate human rights.
"We strongly disagree," Dr Ward Cates of FHI told BBC News Online.
He said the sex workers were offered good medical care.
"The types of care being offered to any of the study participants was well beyond the standard of care offered in Cambodia and in other HIV prevention trials.
"We are providing the participants with an enhanced standard of care."
Dr Cates said he hoped the Cambodian government would reconsider its decision.
The Tenofovir trial has already started in Botswana, Ghana and Malawi. Plans are under way to test the drug on people in the United States, Thailand and Nigeria.
The trial, which is expected to involve 8,000 people, will examine whether it is safe for healthy people to take the drug over a long period.
Another trial will be needed before scientists will be able to say for certain if the drug does or does not protect against HIV.
But Dr Cates is hopeful. "Tenofovir has great promise for further reducing risks of HIV in highly at risk groups," he said.