SHANGHAI, China (AP) — In a reversal of its earlier stance, China's drug safety agency is ordering local authorities to tighten controls on production of heparin, a blood-thinner linked to 19 deaths in the United States and hundreds of allergic reactions.

The State Food and Drug Administration issued the order in a notice, seen Friday on its Web site, that requires heparin producers to obtain the raw chemicals used to make the drug from registered suppliers.

Raw heparin suppliers, meanwhile, are required to improve their management and tests on their products, it said.

Earlier, the Chinese drug agency had insisted that ensuring the quality of exported chemicals like heparin was the responsibility of importers and importing countries.

Heparin is derived from a mucous obtained from pig intestines and other animal tissues, often processed by small, unregistered workshops.

Investigations following the reports of sometimes fatal adverse reactions in the United States, and of similar allergic reactions in Germany, prompted China's new crackdown on unlicensed production.

Earlier this week, the U.S. Food and Drug Administration identified the contaminant in heparin batches from a Chinese supplier to U.S. pharmaceuticals company Baxter International Inc. as oversulfated chondroitin sulfate.

Baxter recalled nearly all its U.S.-sold heparin injections after some patients experienced extreme allergic reactions to the products. There have been similar recalls of Chinese-sourced heparin in Germany and Japan.

Drug safety officials say they have not confirmed yet if the contaminant, which chemically mimics heparin, caused the dangerous allergic reactions.

But both the U.S. and Chinese drug agencies said they were investigating how the oversulfated chondroitin sulfate, which does not occur naturally, got into the heparin batches.

The heparin probe, coming just a year after the toxic chemical melamine was found in a pet food ingredient from China, has refocused attention on various problems with safety and quality of Chinese-made drugs, foods and other products.

China's drug agency has often failed to adequately regulate the country's medicine supplies, and an explosion of production capacity has resulted in numerous reports of adulterated, counterfeit and otherwise unsafe pharmaceuticals.

Last year, China executed the drug agency's director for taking bribes to approve unqualified medicines.

China so far has not reported any adverse allergic reactions to heparin products used in the country.

But the Chinese drug safety agency ordered heparin makers to closely monitor reactions to their products and immediately halt production and recall any products with safety problems.

Deerfield, Ill.-based Baxter International was buying its heparin through a Waunakee, Wis.-based producer, Scientific Protein Laboratories, or SPL, which in turn owns a Chinese factory — Changzhou SPL — and buys additional raw heparin from other Chinese suppliers.

SPL says that the contamination occurred earlier in the supply chain.