Greek forces fired tracer rounds at a Turkish helicopter near the Greek island of Ro in the Aegean Sea on Monday night, in the latest sign of mounting tensions between Athens and Ankara.

The Turkish helicopter provocatively approached the island at low altitude with its lights out, although Greek authorities said it did not actually violate their airspace. Greek troops stationed on Ro fired warning shots at the chopper with tracer rounds from their rifles.

Although the helicopter departed the area without injuries or damage, the Times of London described the encounter as “the most serious crisis between the two countries for 20 years.”

“A night flight with the lights out is part of Turkey’s tactic of provocation from a safe distance which, however, carries the risk of an accident,” the office of Greek Prime Minister Alexis Tsipras said.

The Greek military took a tougher line than the Prime Minister’s office, declaring that “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.”

Relations between Greece and Turkey have grown very tense since the failed July 2016 coup attempt against Turkish President Recep Tayyip Erdogan. Turkey is furious at Greece for refusing to extradite eight Turkish soldiers accused of supporting the coup. Greece is angry at Turkey for detaining and pressing charges against two Greek soldiers who claim to have gotten lost in bad weather during a patrol and wandered into Turkish territory by accident.

An increasingly bitter feud over disputed Aegean islands has some Turkish politicians urging Erdogan to invade and seize the territory from Greece by force.

“We will never allow a ‘fait accompli’ in the Aegean and Eastern Mediterranean and all necessary measures have been taken with determination towards this goal,” Turkish Chief of General Staff Hulusi Akar said on Tuesday, referring to Turkey’s territorial disputes with Greece.

Greek Defense Minister Panos Kammenos last week described Turkey as an “enemy” and dared them to take the islands by force “if they have the guts,” promising that “the Greeks, unified, will crush them.”

Turkey’s EU Minister Omer Celik responded to Kammenos by calling him a “political comedian” and asking the European Union to denounce him.

Erdogan ally and ultranationalist party leader Delvet Bahceli called Kammenos a lunatic in need of psychiatric treatment for his delusions that the gods of Olympus will help him prevail against Turkey. He predicted defeating Greece in the Aegean would be a “piece of cake” if Zeus and his divine progeny do not, in fact, show up for the battle.

Kammenos has described Erdogan as a madman and accused him of kidnapping the Greek soldiers currently held by Turkey for ransom. Turkish officials alternate between absolutely denying any link between the arrest of the Greek soldiers and the Turkish soldiers Ankara wants Greece to extradite and suggesting it would be a lot easier to get those Greek boys home if Athens would extradite the Turks and stop providing a haven for coup conspirators.

Last week saw some hair-raising midair encounters between Greek and Turkish warplanes when Greece accused Turkey of repeatedly violating its airspace. In February, the Turkish navy intercepted a Greek Cypriot ship attempting to conduct oil and gas exploration in the Mediterranean. Also in February, a Turkish coast guard boat rammed a Greek coast guard boat near the disputed islands.