Berlin on Sunday blasted Turkey's President Recep Tayyip Erdogan in a spiralling diplomatic row, saying the strongman had gone too far in accusing Chancellor Angela Merkel of "Nazi practices".

"We are tolerant but we're not stupid," Foreign Minister Sigmar Gabriel told the Passauer Neue Presse newspaper. "That's why I have let my Turkish counterpart know very clearly that a boundary has been crossed here," he added, calling the Nazi comments "shocking".