Chinese drug regulators have accused the manufacturer of the tainted drugs of a cover-up and have closed the factory that produced them. In December, China’s Food and Drug Administration said that the Shanghai police had begun a criminal investigation and that two officials, including the head of the plant, had been detained.

The drug maker, Shanghai Hualian, is the sole supplier to the United States of the abortion pill, mifepristone, known as RU-486. It is made at a factory different from the one that produced the tainted cancer drugs, about an hour’s drive away.

The United States Food and Drug Administration declined to answer questions about Shanghai Hualian, because of security concerns stemming from the sometimes violent opposition to abortion. But in a statement, the agency said the RU-486 plant had passed an F.D.A. inspection in May. “F.D.A. is not aware of any evidence to suggest the issue that occurred at the leukemia drug facility is linked in any way with the facility that manufactures the mifepristone,” said the statement.