"If the allegations were proved true, then it would be completely unacceptable," said Turkish Foreign Minister Ahmet Davutoglu.
"We demand an explanation from the German government and that is our right," he said in a TV interview yesterday.
German weekly news magazine Der Spiegel has reported that Turkey has been a prime target of surveillance by the external intelligence service BND since 2009.
Even though the government usually revises its priority list for surveillance given to the BND every four years, Turkey continued to be on that list until today, it said.
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The Turkish foreign ministry in Ankara said Germany's ambassador Eberhard Pohl was summoned to the ministry yesterday for a discussion on the spying allegations.
The BND's espionage activities are not appropriate to the close relations between the two countries and will cause damage to their joint efforts to safeguard international security and stability, the ministry said in a statement.
Turkey demands an immediate end to the surveillance operations and that has been conveyed to the ambassador, the statement said.
Chancellor Angela Merkel refused to comment on the espionage allegations against the BND.
However, Wolfgang Bosbach, a leader of Merkel's Christian Democrats and chairman of the parliamentary control committee on intelligence services, said the BND's spying on Turkey is "necessary" even though it is a strategic partner of Germany.
Turkey is also a "problematic partner" not just because it has common borders with Iran, Iraq and Syria, but also because several Turkish political organisations such as the banned Turkish Workers' Party (PKK) and some right extremist groups are operating in this country, Bosbach said in a TV interview.
Several leading politicians of both the ruling and opposition parties deplored the alleged espionage by the BND and demanded a speedy clarification from the government.
Hans-Christian Stroebele, Green Party's member of the parliamentary control committee, said if the allegations against the BND were confirmed, he will call for a special meeting of the committee before the end of next month.