"We have received no satisfactory explanation from Austria concerning the incident," foreign ministry spokesman Levent Bilman told reporters.

"We have lodged a complaint before the Organisation for Security and Cooperation in Europe... We will soon lodge a complaint with the United Nations as well," he said.

Asked whether Turkey could scale down its diplomatic and economic relations with Austria, Bilman said: "We are still assessing that."

The man at the centre of the row is Riza Altun, a founding member and chief financial operator of the separatist Kurdistan Workers' Party (PKK), listed as a terrorist organisation by Turkey, the European Union and the United States.

Altun, who is wanted on an Interpol bulletin, emerged in Austria in July after fleeing France, where he was indicted in February for suspected terrorist activities and barred from leaving the Paris region.

Ankara says the Austrian authorities were aware that Altun held fake identity documents and was involved in illegal activities, but still allowed him to board a plane for Iraq, where the PKK enjoys safe haven.

Foreign Minister Abdullah Gul has described Austria's attitude as "a very big mistake" that "erodes the foundations of the international struggle against terrorism."

Ankara is still awaiting a response from Baghdad on a request to extradite Altun, Bilman said.

Turkey has long accused European countries of tolerating PKK activities and failing to close down organisations affiliated to the group.

It says the PKK obtains much of its finances through drug trafficking, people smuggling, extortion and money laundering in Europe, where it has an extensive network.