The overnight incident comes with the erstwhile NATO allies locked in yet another round of tense exchanges, sparked this time by Turkey's detention of two Greek soldiers who according to Athens strayed into Turkish territory by mistake.

"The order to fire the warning shots to force the helicopter to move off came in the context of stepped up surveillance and reaction measures adopted given the increase in tensions with Turkey," the Greek source said.

The source, who asked not to be identified, said the helicopter, apparently operated by the Turkish coastguard, flew along the outer limit of the air control identification zone between the two countries.

The source added that later analysis of radar readings showed that the helicopter had not infringed on Greek airspace.

Recent months have seen a sharp spike in tensions between Athens and Ankara, with Greece determined to protect its sovereign rights in the Aegean where the two sides have a series of longstanding territorial disputes.