The U.S. National Security Agency tapped phone calls involving German Chancellor Angela Merkel and her closest advisers for years and spied on the staff of her predecessors, according to WikiLeaks.

A report released by the group suggested NSA spying on Merkel and her staff had gone on far longer and more widely than previously realized. WikiLeaks said the NSA targeted 125 phone numbers of top German officials for long-term surveillance.

The release risks renewing tensions between Germany and the United States a month after they sought to put a row over spying behind them, with U.S. President Barack Obama declaring in Bavaria that the two nations were "inseparable allies."