China's agricultural ministry will further step up its oversight of genetically modified technology research institutes and biotechnology companies to prevent commercial cultivation of unauthorized varieties.

The Ministry of Agriculture said in a statement after a work conference on March 31 that it will further increase oversight of GM crops in the research and experiment, varietal registration and seed production phases.

It came after a report by environmental nonprofit organization Greenpeace in January that claimed that farmers were illegally growing genetically modified corn in China's Northeast.

The organization claimed that 93 percent of samples taken last year from corn fields in five counties in Liaoning province tested positive for GM contamination.

The agricultural ministry said it will try to ensure all science and research activities involving GM technology are in line with laws and regulations, and ensure that the production of seeds are traceable.

China's agricultural authorities have to approve the marketing of GM grains, with only domestic GM papaya and cotton being approved for commercial cultivation.

Han Jun, deputy director of the Office of the Central Rural Work Leading Group, China's top rural affairs decision-making agency, said in a news conference in January that the country has investigated and treated cases of farmers illegally growing GM rice, and the cases indicated that there should be stronger efforts to prevent such illegal activities.