Chinese officials voiced doubts Monday that a contaminant identified in the blood thinner heparin was the root cause of severe allergic reactions in hundreds of Americans.

The officials suggested at an embassy news conference in Washington that the problem with the drug could have occurred in the United States. They plan to visit a Baxter International plant in New Jersey to get a better picture of how the finished product is manufactured.

"When you see it, then you believe it," said Jin Shaohong, the deputy director general for the National Institute for the Control of Pharmaceutical and Biological Products in China.

Heparin is derived from a mucus obtained from pig intestines and other animal tissues, often processed by small, unregistered workshops in China. Scientific Protein Laboratories owns a Chinese factory — Changzhou SPL — and buys additional raw heparin from other Chinese suppliers.

The Chinese officials said Changzhou SPL, the manufacturer of the heparin ingredient, was managed and overseen by a manager from Scientific Protein Laboratories' headquarters in Wisconsin, and the manufacturing processes and quality control were all provided by SPL's headquarters.

The U.S. Food and Drug Administration says 62 deaths have been associated with allergic-type reactions to contaminated batches of heparin.

The FDA can't say for sure what caused the reactions, but the chief suspect is a contaminant that the agency discovered in supplies of raw heparin coming from China.