Japan and South Korea suspended some imports of American wheat, and the European Union urged its 27 nations to increase testing, after the United States government disclosed this week that a strain of genetically engineered wheat that was never approved for sale was found growing in an Oregon field.

Although none of the wheat, developed by Monsanto Company, was found in any grain shipments — and the Department of Agriculture said there would be no health risk if any was shipped — governments in Asia and Europe acted quickly to limit their risk.

South Korea, which last year purchased roughly half of its total wheat imports of five million tons from the United States, said Friday it would suspend purchases until tests were performed on arriving shipments. Results of the tests, by the Ministry of Food and Drug Safety, were expected in the first week of June, according to local media.

Seoul also raised quarantine measures on wheat for livestock feed, while Thailand put ports on alert.