German Chancellor Angela Merkel said Monday that if reports a German intelligence employee spied for the United States are proven true, that would be a "clear contradiction" of trust between the allies.

Speaking at a news conference in China, Merkel made her first public comment on the arrest last week of a 31-year-old man suspected of spying for foreign intelligence services.

German prosecutors say the man is suspected of handing over 218 documents between 2012 and 2014. German media, without naming sources, have reported he was an employee of Germany's foreign intelligence service who says he sold his services to the U.S.

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"If the allegations are true, it would be for me a clear contradiction as to what I consider to be trusting co-operation between agencies and partners," Merkel said at a news conference in Beijing with the Chinese premier.

Germany has been stepping up pressure on the United States to clarify the situation. The issue threatens to strain German-U.S. relations again after earlier reports that the National Security Agency spied on Germans, including on Merkel's cellphone.

The German newspaper Bild reported Monday that German Interior Minister Thomas de Maiziere wants to include the U.S. among future German spy targets in response to the case.

German Foreign Minister Frank-Walter Steinmeier said if the allegations of U.S. involvement were true, the case could lead to unspecified changes in the two countries' "daily routine."

"Should the suspicions be confirmed that American intelligence agencies were involved, then that's also a political matter where one can't just go back to the daily routine," said Steinmeier during a visit to Mongolia, according to his office.

"We will work hard to answer the outstanding questions and then decide how to react," he said. "I hope that the U.S. can contribute to resolving this matter as quickly as possible."