BERLIN (AP) — Germany summoned the U.S. ambassador in Berlin on Friday following the arrest of a man reported to have spied for the United States, heightening friction between the two countries over alleged U.S. eavesdropping in Germany.

U.S. Ambassador John B. Emerson was called in “in connection with an investigation by the federal prosecutor,” the German Foreign Ministry said in a statement. The U.S. envoy “was asked to help in the swift clarification” of the case, it added.