China rejected a cargo of U.S. corn because it contained a genetically modified variety that is not approved for import, a trade source said Monday.

The shipment contained Syngenta AG’s Agrisure Viptera corn, also known as MIR 162, the source said.

“It’s confirmed. It’s one cargo and MIR 162 was the problem,” said the source, who asked not to be identified.

China has not yet signed off the variety but is expected to approve it later this year or in 2014, according to traders. It is approved for import by numerous U.S. trading partners, including Mexico, the European Union and top corn importer Japan.

“Syngenta is not aware of any such incident,” said Paul Minehart, head of corporate communications-North America for Syngenta Corp.

Agrisure Viptera, designed to offer enhanced protection against crop-damaging insects, is widely grown in the U.S. so traces of the grain may have been commingled with approved corn strains in a shipment to China, traders said.

A bulk corn shipment from Argentina was cleared for import earlier this year despite it containing traces of MIR 162.

China is expected to import a record-high seven million tonnes of corn in the 2013-14 marketing year, according to the U.S. Department of Agriculture.

After shifting from a corn exporter to a net importer in 2010, China has become on of the world’s top three corn markets, buying nearly all of its imports from top exporter the United States.

— Karl Plume reports for Reuters from Chicago.