The German government faced an angry response by Turkey on Monday after reports that Berlin’s intelligence agency spied on its NATO partner.

Authorities in Ankara summoned the German ambassador to demand answers, with Turkish Foreign Minister Ahmet Davutoglu saying that if found to be true, the espionage would be “unacceptable, inexcusable.”

It follows reports in Der Spiegel that the German intelligence agency, known by its acronym BND, had inadvertently listened to calls made by U.S. Secretary of State John Kerry and his predecessor Hillary Clinton – the kind of activity for which Chancellor Angela Merkel has criticized Washington. The magazine also cited a confidential 2009 BND document listing Turkey as a target for intelligence gathering, but didn't say what that spying involved.

Turkey said it had asked for a full explanation from German Ambassador Eberhard Pohl.

"It is expected that the German authorities present an official and satisfactory explanation on the claims reported by German media and end these activities immediately if the claims are true," the Turkish foreign ministry said in a statement.

German officials would not confirm Der Spiegel's report. Government spokeswoman Christiane Wirtz said only that the government in July informed a parliamentary intelligence committee about some of the matters in the report and would inform it about the rest soon. The panel is sworn to secrecy.

Last October, after reports surfaced that the United States had been monitoring her mobile phone, Merkel said that "spying among friends is not at all acceptable.”

The chancellor, asked about the spying reports during a visit to Latvia on Monday, said she could not comment on the activities of the intelligence services and made clear that her comment about spying on friends had been made with the special context of the German-American relationship in mind.

Some German lawmakers defended the idea of spying on Turkey. Christian Flisek, of the governing Social Democrats, noted that it is "a geopolitically important country."

The German opposition now accuses the government of hypocrisy. Greens party co-leader Simone Peter said it was "incomprehensible" that Germany should be "actively spying on allied states" after the outcry about the NSA's activities.

Germany is Turkey's largest trading partner in the European Union and is home to some three million Turks. But relations are not always smooth and Merkel's conservatives are skeptical about Turkish EU membership.

Wire services