Merkel on Monday joined in a chorus of German politicians voicing their concern over the arrest of a German intelligence employee for allegedly spying for the US.

"If the reports are correct it would be a serious case," Merkel said. "If the allegations are true, it would be for me a clear contradiction as to what I consider to be trusting cooperation between agencies and partners."

Last week, German police arrested an employee of Germany’s foreign intelligence service, the BND, on alleged charges of spying for the United States. According to German media, the arrested BND employee is believed to have passed over 218 scanned documents since 2012.

Germany’s Interior Minister Thomas de Maiziere said in an interview with German daily Bild on Monday that the government wants a quick and clear explanation from Washington regarding the issue.

In addition, German President Joachim Guack warned on Sunday of further strains in German-US relations if the suspicions are confirmed.

This comes as a German parliamentary inquiry is currently being held to assess the extent of spying by the US National Security Agency (NSA) and its partners on Germans, and whether German intelligence aided the activities.

Last month, German federal prosecutors opened a criminal investigation into alleged unlawful US surveillance of Chancellor Angela Merkel’s mobile phone communications.

RA/NJF