Iran briefly closed its airspace to German Chancellor Angela Merkel's plane as she flew for a visit to India on Tuesday, delaying her arrival and sparking a diplomatic row.
Merkel was held up as she flew overnight on Monday-Tuesday for a meeting with Indian Prime Minister Manmohan Singh and President Pratibha Patil in New Delhi.
"Hindering the German chancellor's passage over Iran is absolutely unacceptable. It shows a lack of respect towards Germany that we will not accept," Foreign Minister Guido Westerwelle said in a statement.
He summoned the Iranian ambassador in Berlin to "make it very plain that such a breach of international conventions will in no way be tolerated by Germany."
The reasons for the delay were not immediately known and a second plane with four of Merkel's ministers and other delegation members was not held up.
Merkel, speaking at a news conference with Singh, declined to go into detail about the inconvenience, which saw her plane circle for two hours over Turkey before receiving permission to cross Iran, according to reports.
"I am very glad I arrived safely here," she said. "Everything has turned out excellently. We got to hold the Indo-German consultation. That is the most important thing."
Her troubled arrival overshadowed the meeting with Singh, during which the two leaders agreed to strengthen economic ties between Europe's biggest economy and one of the world's fastest-growing markets.
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They also discussed regional security and Afghanistan, where Germany has been reported to be helping mediate secret, direct talks between the United States and the Taliban.
Merkel stressed that Germany would host the next Afghanistan conference at the end of the year and was seeking reconciliation of all forces in the country "if those forces fulfil all conditions such as renouncing the use of force."
The German leader also pressed the case for the Eurofighter Typhoon fighter jet, made jointly by a European consortium including Germany, which is competing for a $12 billion deal up for grabs in India.
"We are convinced that we have the best product on offer compared with others," she told reporters.
The Eurofighter is up against the France-made Rafale produced by defence contractor Dassault.
Germany is India's biggest trading partner in Europe, with bilateral trade at 15.4 billion euros ($21 billion) in 2010. Indian officials forecast that this figure will grow to 20 billion euros by 2012.
The meeting came a day after Germany announced it would phase out its atomic plants by 2022, a global first by a major country in the wake of the disaster in March at Japan's Fukushima plant.
India, meanwhile, has announced plans to dramatically increase its nuclear power capacity and has been in talks with Russian, French, Japanese and US groups to build new plants across the country.
At present, three percent of India's electricity comes from nuclear power but the government wants to increase that to six percent by the end of the decade and 13 percent by 2030.