The German newspaper Der Spiegel had reported a U.S. surveillance program targeted EU computer systems. The allegation was part a controversial surveillance program leaked to the media by former U.S. National Security Agency employee Edward Snowden.
Ashton said in a statement Monday she was aware of the reports and had contacted U.S. authorities seeking "urgent clarification" on the issue.
"The U.S. authorities have told us they are checking on the accuracy of the information released yesterday and will come back to us as soon as possible," she said in a statement. "While this is clearly a matter for concern, we will make no further comments at this stage, until we have more clarity on the matter."
Members of the European Parliament expressed concern about the surveillance program dubbed Prism during June debates in Strasbourg, France.
The French government was less conciliatory than Ashton.
French Foreign Minister Laurent Fabius said the allegations were "totally unacceptable" if confirmed.
"We expect the American authorities to promptly address the legitimate concerns raised by these revelations in the press," he said.