An attempt to sue authorities in China's northwestern Xinjiang region over discrimination against children infected with the Hepatitis B virus has foundered after parents dropped the case under what activists say was heavy pressure from local officials.

The failure of the lawsuit highlights the difficulties faced by Chinese who seek to challenge local authorities in the courts, even in cases where officials appear to be defying national policy.

Parents of seven Hepatitis B-infected children recently expelled by a top school in Urumqi, the capital of Xinjiang, sued city education authorities to compel them to allow the children to resume their studies.

The children were among a group of 19 expelled students despite a national ban on discrimination against the estimated 120m Chinese who carry the Hepatitis B virus, which is mainly transmitted at birth, through sexual contact, or by use of contaminated needles.

China's health ministry says carriers can live, work and study normal, but Urumqi officials have defended the expulsions as necessary to protect other pupils and have banned the local student-led health education group that first publicised the case.

"The families of the seven pupils involved in the lawsuit came under pressure from local government departments to withdraw it," said Lu Jun, a health activist and organiser of a popular website for Hepatitis B carriers.

Some parents had been taken to local police stations and told to put their seal on pre-prepared forms applying for the lawsuit to be withdrawn, and some who refused had been subjected to round-the-clock close surveillance, Mr Lu said.

Another person familiar with the case also said harassment by local authorities had forced the families to drop the suit.

Court officials and Xinjiang police declined to comment. The families of the expelled pupils could not be reached yesterday.

Zhang Yuanxin, a lawyer representing the families, declined to comment on the treatment of the plaintiffs.

However, he said he had been ordered not to make contact with his clients and had only heard about the withdrawal of the lawsuit when informed by the district court.

The expulsions were a disaster for pupils who had won coveted subsidised boarding places at the Urumqi No. 15 Middle School but have since had to return to home villages and towns with vastly inferior educational facilities.

Mr Zhang said the lawsuit had offered the possibility of an independent review of local authorities' judgement of the threat posed by Hepatitis B. "Without a clear verdict, I think similar cases will continue to happen in Xinjiang," he said.

Activists say prejudice against virus carriers has grown in recent years amid confusion about how it is transmitted and widespread advertising of Hepatitis B treatments which has stoked public fears about the disease.

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