There's been a large-scale confrontation between Greece and Turkey in the skies over the Aegean Sea. Greece said more than 25 Turkish fighter jets violated Greek airspace early today and an equal number of Greek planes had been sent to intercept them. A Greek government spokesman Dimitris Repas said the Turkish planes were not taking part in the joint exercises currently being held by Turkey, Israel and the United States. Our Defence Correspondent Jonathan Marcus looks at the continuing tensions between these two key countries on NATO's southern flank.

The Greek Government's claims that Turkish jets entered air space over the Aegean supervised by the Greek air traffic control authorities are difficult to substantiate. The Greeks say that they scrambled over 20 fighters to intercept the Turkish planes.

And if the reports are true, they do involve an unusually large number of Turkish aircraft. The alleged incursions fit into a regular pattern of similar incidents - a dangerous game of cat and mouse - that on occassion threatens to bring these two NATO members into open conflict.

It is Turkey's large-scale manoeuvres in the Aegean that have prompted today's episode. Such exercises always increase tension.

But there is an additional political aspect to the crisis. Turkey feels that it has been rebuffed in its attempts to join the European Union, of which Greece is already a part.