(Reuters) - U.S. health regulators said on Friday a third cancer-causing toxin was found in some blood pressure pills recalled by India’s Hetero Labs Ltd a day earlier, adding to a global recall of commonly used drugs to treat hypertension.

FILE PHOTO: A man has his blood pressure checked at the Remote Area Medical Clinic in Wise, Virginia, U.S., July 22, 2017. REUTERS/Joshua Roberts

The U.S. Food and Drug Administration is also looking into whether these types of impurities could be found in other classes of drugs, a spokeswoman for the regulator said.

The toxin, N-Nitroso-N-methyl-4-aminobutyric acid (NMBA), identified in 87 lots of Hetero’s losartan potassium pills, was not found in medicines that were previously recalled by a number of drugmakers.

The FDA said Torrent Pharmaceuticals Ltd is expanding its voluntary recall to include 114 additional lots of losartan-containing medication due to unacceptable amounts of NMBA in the losartan manufactured by Hetero Labs.

Global authorities have been clamping down on sales of some blood pressure medicines as they are suspected to be tainted with two probable carcinogens - N-nitrosodiethylamine (NDEA) and N-nitrosodimethylamine (NDMA).

The drugs, including losartan, belong to a class of widely used medicines for treating high blood pressure called angiotensin II receptor blockers, or ARBs. Some generic versions of other ARBs, such as valsartan and irbesartan, have also been recalled.

The FDA said increased risk of cancer in patients exposed to the new impurity, NMBA, appeared to be the same as those exposed to NDMA, but less than the risk from NDEA.

The recalls began last year after regulators said ingredients used by Chinese manufacturer Zhejiang Huahai Pharmaceuticals Co to produce valsartan contained cancer-causing impurities.

Since then, generic drugmakers such as Mylan NV, Teva Pharmaceutical and Novartis’ Sandoz have recalled products containing the tainted ingredients.

In January, the FDA warned of the possibility of additional shortages of hypertension drugs in the United States due to the recalls.

The FDA also said it is working to develop testing methods to detect other cancer-causing impurities.