(Reuters) - India's Strides Pharma Science Ltd said on Friday it has halted sales of its heartburn drug Ranitidine in the U.S. market as it conducts tests to identify possible cancer-causing impurities in the tablets.

The move comes after the U.S. Food and Drug Administration (FDA) asked the company to test the drug for indications of N-nitrosodimethylamine (NDMA) impurity, which the regulator says is a "probable human carcinogen".

Earlier this week, Dr. Reddy's Laboratories Ltd and GlaxoSmithKline Pharmaceuticals Ltd halted Ranitidine distribution, while global companies such as Novartis AG have stopped the supply of their versions of the drug.

The FDA flagged the presence of NDMA in Ranitidine samples two weeks ago, while European regulators were assessing its presence in the drug.

Meanwhile, the Canadian drug regulator said the lots of medicines being recalled may have been made using an active ingredient containing NDMA above accepted levels, as it urged companies to stop distributing Ranitidine.

(Reporting by Nallur Sethuraman in Bengaluru; Editing by Subhranshu Sahu)