Six hours of talks Thursday in Berlin, spurred by the Japanese disaster, failed to reach an agreement, the EUobserver reports.
EU Energy Commissioner Guenther Oettinger, supported by his homeland, Germany, along with Italy and Sweden, said terrorism threats must be included in screening Europe's 143 nuclear power plants.
But French and British representatives said the reactors should be examined only on their ability to withstand natural disasters.
"No final decision has been taken," Oettinger's spokeswoman Marlene Holzner said. "Commissioner Oettinger was very clear on that. He said he would like terrorist attacks and other man-made disasters included in the tests. He would like to start as soon as possible, but for the credibility of the tests, the content is more important than the timing."
Officials will try again to reach an agreement in Prague next week.
Delay could prevent the European Commission from presenting a report on the state of nuclear plants in December, as planned.