NATO allies Turkey and Greece are facing off in one of their fiercest rows in months over a wealth of energy deposits in the eastern Mediterranean Sea.
It is far from the first time tensions have flared between the two uneasy neighbours. Here is a look back at their difficult recent history.
Turkey and Greece have been at loggerheads over territorial boundaries in the sea for decades.
Much of the tension over the Mediterranean can be traced back to their dispute over Cyprus, which was invaded by Turkey in 1974 in response to an Athens-engineered coup, which sought to unite the island with Greece.
The Greek speaking south is the Republic of Cyprus that became a member of the European Union in 2004.
The internationally-unrecognised Turkish statelet in the north is split from the south by walls, barbed wire and sandbags.
The "Green Line" is patrolled by UNFICYP, one of the United Nations' oldest peacekeeping forces.
Turkey says it is ready to negotiate with any country -- including Greece -- except for the Republic of Cyprus, which it does not recognise.
The Cyprus dispute has now widened across a number of issues, including the right to disputed waters and airspace.
Greece argues that international law gives it the right to extend its territorial seas to 12 nautical miles from the present six, but Turkey fears this could cut off its access to the Aegean continental shelf and its oil and natural gas.
The Aegean Sea has a complex geography with a web of more than 2,000 islands, most of them Greek.
The two countries came to the brink of a war in the 1990s over a pair of small uninhabited islets known collectively as Kardak in Turkish and Imia in Greek.
But those tensions were set aside with the so-called earthquake diplomacy of 1999, where Greece responded to a devastating earthquake in Turkey.
The Syrian war has triggered an influx of refugees, especially to Turkey, a transit point for many seeking to reach prosperous EU nations. Turkey is now providing a home to around four million refugees -- the majority of them Syrian.
More than one million refugees arrived in the EU in 2015.
The crisis could only be resolved a year later after Ankara signed a landmark deal with the EU to stop the flow in return for incentives that included financial assistance.
But President Recep Tayyip Erdogan has long used the threat of opening Turkey's borders to migrants as a way of wringing concession in disputes with Brussels.
In February, he allowed refugees to cross into Greece, leading to border skirmishes.
The discord on how to handle Byzantine heritage inside Turkey has cracked open an old schism between the two countries.
The worries deepened after Turkey last month reconverted Istanbul's Byzantine-era Hagia Sophia into a mosque, stripping its museum status -- which had been in place since the 1930s as the new Turkish republic sought a more secular course.
Greece lashed out at Ankara's move to reopen the UNESCO World Heritage site for Muslim worship, with Prime Minister Kyriakos Mitsotakis calling it a demonstration of Turkey's "weakness".
Erdogan has been placing an ever greater emphasis on lavish celebrations marking the defeat of the Christian Byzantines by the Muslim Ottoman Turks.
This month, he ordered another ancient Orthodox site that became a mosque and later a museum to be turned back into a place of Muslim worship.
Turkey claims Greece fails to take care of the rights -- including in education -- of the Muslim minority in Western Thrace, a central region of Greece.
Erdogan has often accused Greece of mistreating the Muslim and Turkish-speaking minorities on its territory, and singled out Athens as the only European capital without an official mosque.
Athens, in turn, is pressing Turkey to open an Orthodox clergy school in an island off Istanbul.
Ankara also does not recognise the "ecumenical" title of the Greek Orthodox Patriarch in Istanbul.
The flight of Turkish military soldiers after a 2016 coup attempt against Erdogan's government has become another source of friction.
In 2017, a Greek court turned down Turkish demands to extradite eight former Turkish army officers.
The eight fled to Greece by military helicopter on the night of the putsch, which Turkey says was masterminded by the US-based Islamic preacher Fethullah Gulen.