Iran set off a diplomatic row with Germany on Tuesday by closing its airspace to Chancellor Angela Merkel's plane as it flew to India and delaying her arrival there on an official visit.
Germany summoned the Iranian ambassador in Berlin to protest "the breach of international protocol," said Foreign Minister Guido Westerwelle.
"Iran's move to hinder the chancellor's trip is absolutely unacceptable," he said in a statement. "This is a lack of respect for Germany that we won't accept," said Westerwelle, who was on an official trip to Australia.
Iran had granted overflight permission to Merkel's plane before it left Berlin, but that was revoked after the chancellor was airborne, the German government said.
Merkel's plane was forced to circle over Turkey for about two hours en route to India, said German government spokesman Steffen Seibert. He called it a violation of normal diplomatic privilege that Merkel had never experienced before.
A deputy foreign minister, Wolf-Ruthart Born, told Iran's ambassador that the refusal was "an unprecedented incident" that must never happen again, the Foreign Ministry said.
According to the ministry, Iran said the delay occurred because of unspecified "technical and organizational developments" and the ambassador assured Born that he would inform his government immediately of Germany's position.
A second plane carrying several of Merkel's ministers had no trouble transiting Iranian airspace on the way to the government consultations in India.
Christoph Heusgen, Merkel's top security and foreign policy adviser, led negotiations with Iran from aboard Merkel's plane and it was eventually allowed to fly over Iran, German news agency DAPD reported.
Germany is part of the group of six nations negotiating with Iran over its nuclear program. The government in Berlin also supports sanctions against Iran, and a Germany-based Iranian bank was recently added to an EU sanctions list.
Iran is suspected of covertly developing nuclear weapons, but it has denied that.
The flight marked Merkel's first official trip aboard her newly revamped government Airbus A340 Konrad Adenauer, Germany's equivalent to the U.S.'s Air Force One.