The three activists who disappeared last month were investigating conditions at factories owned by Huajian. The chairman of Huajian, Zhang Huarong, strongly denied in an interview in December that his company had broken any labor laws, and company spokesmen have reiterated that in recent days.

Hours after the statement from the United States, a lawyer for one of the activists was allowed to hold a 90-minute lunchtime meeting with his client at a detention center in Ganzhou in southern China. The lawyer, Wen Yu, said he had previously been turned away twice in attempts to meet his client, Hua Haifeng.

Mr. Wen said that his client described being kept in a room crowded with about 20 suspects in various criminal cases. Mr. Hua had to sleep just a foot from a bucket that detainees used to urinate during the night, and the smell and noise made it hard for him to sleep, Mr. Wen said.

Mr. Wen said that a second investigator who had also been in Ganzhou, Su Heng, was being detained in a different room at the same center, and had a different lawyer representing him.

Mr. Hua’s wife, Deng Guilian, said she had asked a guard at the detention center if a third investigator, Li Zhao, was also being held there and the guard had said yes. But Mr. Wen said he had not heard of any lawyer being named to represent Mr. Li.

A spokesman for the Ganzhou police, who gave only his surname, Wu, declined to comment on the men’s cases and referred questions to a municipal propaganda office. Reached by phone, an official there had no immediate response.

Mr. Hua is accused of illegal use of eavesdropping or photographic equipment, Mr. Wen said, while the accusations against the other two men have not been officially confirmed. China Labor Watch said the three men were not engaged in illegal activity; Mr. Wen said his client had used a cellphone in the factory to take photos but added that this was legal.