A trilateral commission has recommended that Mexico enact stricter controls over genetically modified (GM) U.S. corn that has been winding up in the fields where the crop was first developed thousands of years ago.

The environmental activist group Greenpeace made the study's findings public Monday at a press conference in front of the Environment Secretary.

Greenpeace Mexico director Alejandro Calvillo said that the governments of Mexico, Canada and the United States had been holding back on releasing the report, which could influence a global debate over the safety of GM foods.

The study from the North American Commission for Environmental Cooperation (CEC) recommends Mexico enact precautionary measures to prevent the further spread of GM corn, including grinding up U.S. corn imports.

The group of scientists assembled by the CEC, a watchdog group set up under NAFTA, said if the transfer of GM genes to native corn is left unchecked, GM varieties could eventually displace native species.

The U.S. and Canadian governments, as well as GM industry groups, have strongly criticized the science used in the report.

The CEC report said Mexico should maintain its moratorium on planting GM corn, carry out studies to measure the impact of the GM corn that has already been planted, and enact stricter controls on GM corn entering the country from the United States, Greenpeace said in a statement.

The conclusions were drawn up by 15 scientists from the three countries that make up the North American Free Trade Agreement.

The study was carried out at the request of 22 communities in the southern state of Oaxaca, where strains of GM corn were discovered in isolated, rural corn fields in 2002.

Calvillo said the governments had agreed to make the study public after it was certified by the commission in June but had not done so yet.

The U.S. government has denied it is trying to bury the report, saying it is raising concerns over the quality of the scientific evidence within a 60-day review period.

That period expired at the end of August.

"The unjustified delays in its publication only respond to the interests of GM promoters, not that of society as a whole," Calvillo said.

He said the U.S. government feared the publication of the report could unfavorably influence its legal challenge before the World Trade Organization over the European Union's ban on GM imports.

Calvillo also alleged the Mexican administration, which Greenpeace accuses of pandering to biotech companies, wants to prevent any conclusions from the study from affecting a bio-security bill currently being drawn up in Congress.

The discovery of strains of GM corn in Oaxaca came as a surprise since a moratorium on planting GM corn has been in effect since 1998. The discovery alarmed environmental and farmer activists.

While the United States backs the use of GM crops, other nations, especially European countries, have expressed concerns about the technology.

Activists say the "contamination" of Mexican fields with GM corn could lead to yet unknown effects on native corn varieties and ecosystems.

"Corn embodies deep Mexican cultural values that should be respected and protected," said Areli Carreón, director of Greenpeace's consumer campaign in Mexico. "Most campesinos don't receive benefits from GM corn and view its presence in their native crops as a threat to their form of life."

U.S. agricultural companies like Archer Daniel Midlands are expected to export over 6 million tons of corn to Mexico this year. From 30 to 50 percent of the grain is estimated to be GM corn.

While the GM corn is supposed to be used for animal feed or industrial uses, activists complain there are no safeguards in place.