Cargill Inc., the top exporter of U.S. grain and oilseeds, said it will reject crops containing a new genetically modified Syngenta AG corn trait that are delivered to its grain elevators for export contracts.

Corn seeds containing Syngenta's Agrisure Duracade trait are available for planting in the U.S. for the first time this year after U.S. authorities cleared the trait in 2013. The trait has not been approved for import by China or the European Union, both major buyers of U.S. crops.

Duracade has import approval from some other big buyers, including Mexico, South Korea and Japan.

"For export contracts, we will not accept delivery of any commodity containing the Duracade trait," Cargill told Reuters in an email.

"Cargill reserves the right to reject and/or require testing of deliveries and any acceptance, rejection or testing for the presence of Duracade will be determined by Cargill in its sole discretion at the time of delivery," the company said.

The commercialization of Duracade has split the U.S. farm sector and pitted global grain merchants against Swiss-based Syngenta, the world's largest crop chemicals company. Some U.S. growers say they need access to the new trait, which is engineered to fight pests called rootworms, while exporters warn it threatens to disrupt trade.

Bunge Ltd, one of the world's top agricultural trading houses, signaled it will refuse to handle crops containing Duracade unless the product is cleared by China.

Since November, China's authorities have rejected more than 600,000 tons of U.S. corn and corn products containing another unauthorized genetically modified Syngenta corn trait, Agrisure Viptera. Known as MIR 162, the trait has been awaiting Beijing's approval for more than two years.

China has begun testing imported U.S. soybean cargoes at the southern province of Guangdong for contamination with the MIR 162 strain of corn, traders said this week.

"At our grain elevators, we will continue to ask farmer customers to give us advance notice if they will deliver Viptera," Cargill said. "This coming crop year, we are asking the same for Duracade."

The National Grain and Feed Association and North American Export Grain Association last month asked Syngenta to suspend the commercial use of Duracade and MIR 162 in the United States until China and other U.S. export markets have granted regulatory approval.

Syngenta has declined the request, saying Duracade will be available in limited quantities and that growers need new technologies.

The company has said it commercializes corn traits in line with industry practices, once it has approval from countries with "functioning regulatory systems."

Even if corn containing Duracade is planted on a small number of acres, it could accidentally be shipped to China, exporters have noted. Varieties are often mixed with each other because they are grown in fields close to each other and then harvested, transported and stored together.

The U.S. is expected to export 1.6 billion bushels of corn in the marketing year that ends on Aug. 31, accounting for 11% of the last harvest. The rest of the crop will be used domestically to feed livestock and produce ethanol.