For almost half an hour, 13 aircraft vanished from air traffic controllers' radar screens as they flew at high altitude above Europe, it has been revealed.

The "undprecedented" disappearances happened on 5 June and 10 June, hitting control rooms in Austria and neighbouring countries.

The relevant EU agencies have been asked to investigate, Austria's flight safety organisation said on Thursday. Marcus Pohanka of Austro Control said the height, location, identities and other information for a total of 13 aircraft suddenly vanished.

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He said several neighbouring countries had similar incidents and the EU's Eurocontrol and European Aviation Safety Agency has been asked for a probe. He did not identify the other nations. but the daily Kurier said flight controllers in Munich and Karlsruhe in Germany, and in Prague, the Czech Republic, also reported related problems.

The newspaper cited unnamed experts as saying interference between the aircrafts' transponders and ground control was apparently to blame. Pohanka declined to confirm that or to say which airlines and planes were involved. But he suggested that at least some may have been long-distance passenger aircraft, based on their high altitudes.

There was no danger at any time, he said, adding that extra air controllers were immediately called to their posts, where workers established voice contact with pilots and widened flight corridors.