2020 has been the most acrimonious year for Greek-Turkish relations since 1974. Here, we review the key events that led to the fallout:

January 2: East Med pipeline deal signed

Greece, Cyprus and Israel signed an agreement to build the Eastern Mediterranean Pipeline that will carry natural gas 1,900km from the Eastern Mediterranean basin to the European market. The pipeline is estimated to cost 7bn euros ($8.53bn) and carry an initial 10 billion cubic metres annually, expandable to 16 billion cubic metres annually. It is a major irritant to Turkey, which sees it as an attempt to exclude it from the region’s energy bonanza.

January 30: Turkish ship enters contested waters

The Turkish seismic survey ship Oruc Reis entered Greece’s Exclusive Economic Zone southeast of Karpathos for about 24 hours, testing Greek reflexes. It was monitored by the Greek frigate Nikiforos Fokas.

February 27: Turkey opens borders to Europe-bound refugees

Turkey announced it was opening its borders to refugees bound for Europe, triggering the biggest refugee crisis in five years. For two weeks, Turkey gave free passage on the country’s buses and trains to refugees travelling to the Greek border. During that time, Greece says it resisted more than 42,000 attempted entries at the land border and an unspecified number at sea. Turkey posted footage of the Hellenic Coast Guard preventing refugee-filled boats from reaching Greek waters. By March 9, Greece registered 2,164 successful crossings, of which 313 were by land and 1,851 by sea.

April 15 – May 11: Refugee crisis escalates, both sides reinforce borders

Greece notified Turkey that it was extending its border fence at the Evros river to secure its border against further refugee crises. On May 11, Turkey warned Greece against trespassing on Turkish soil. Both sides sent border reinforcements, highlighting tensions.

June 9: Greece signs EEZ agreement with Italy

Greece signed an Exclusive Economic Zone agreement with Italy, which had been under negotiation for four decades. The agreement follows the principles of the United Nations Convention on the Law of the Sea (UNCLOS), allowing Greece’s islands a full EEZ – something Turkey disagrees with.

July 13: Greece raises issue of sanctions over Hagia Sophia

Greece first raised the issue of sanctions against Turkey at the EU General Affairs Council, for converting the Church of Hagia Sophia into a mosque. Foreign Minister Nikos Dendias said he also warned his EU counterparts that Greece might invoke the mutual defence clause of the EU’s basic treaty (Treaty on the European Union, article 42) over the summer. Turkey had threatened to carry out exploration for oil and gas on what Greece considers its continental shelf under international maritime law (UNCLOS).

July 21: Turkey issues warning over East Med

Turkey issued a navigational telex warning of further exploration in what Greece considers its Exclusive Economic Zone, sparking a full deployment of the two countries’ navies across the Aegean and in the East Mediterranean.

August 6: Greece announces EEZ agreement with Egypt

Amid attempts to restart exploratory talks with Turkey, Greece announced an Exclusive Economic Zone agreement with Egypt. This irritated Turkey, because it covered the same body of water Turkey had divided up with Libya the previous year, in an agreement the US and EU denounced as irregular. The Greece-Egypt deal follows the Law of the Sea, allowing Greece’s islands an EEZ. Turkey called off the exploratory talks and announced live-fire exercises in the East Mediterranean.

August 12-13: Frigates collide, France boosts presence in East Med

The Greek frigate Limnos and the Turkish frigate Kemal Reis collided in an apparent accident, damaging the latter. In reaction, France’s President Emmanuel Macron said he was temporarily boosting the French military presence in the Eastern Mediterranean amid mounting tensions with Turkey.

August 26: Greece announces extension of territorial waters

Greek premier Kyriakos Mitsotakis unexpectedly announced the imminent extension of Greece’s territorial waters off its west coast to the full 12 nautical miles allowed under maritime law, sending a clear message of its intent to do the same in the Aegean. Currently Greece claims six nautical miles.

August 27: Greek parliament ratifies EEZ agreements with Italy, Egypt

August 28: EU foreign ministers draft sanctions against Turkey ahead of EU summit

An informal council of EU foreign ministers in Berlin agreed on a list of sanctions designed to stop what they deem unauthorised Turkish drilling in the East Mediterranean. The sanctions, which started by targeting ships, companies and individuals involved in supplying illicit drilling in the East Mediterranean and graduated to freezing EU disbursements to Turkey and EU bank credit to Turkish businesses, were to be activated by an EU summit on September 24.

September 3: NATO chief steps in

NATO secretary-general Jens Stoltenberg asks Greek and Turkish representatives to a meeting to discuss deconfliction mechanisms in the region. No such agreement has yet been signed.

September 10: EU members condemn Turkish actions

Seven Mediterranean EU members (Med7: Portugal, Spain, France, Malta, Italy, Greece, Cyprus) condemned Turkish actions when they met on Corsica for their annual summit. The Med7 statement expressed “full support and solidarity with Cyprus and Greece in the face of the repeated infringements on their sovereignty and sovereign rights, as well as confrontational actions by Turkey”.

September 12: Greek PM announces first defence spending in over a decade

Mitsotakis announced Greece’s first defence spending increase in 12 years. Greece would immediately purchase 18 fourth-generation Rafale fighter jets, to replace its 43 Mirages-2000 fighters, and two used frigates. In the medium term, it would order four new frigates and upgrade its four newest, MEKO-type frigates, thus replacing an ageing fleet of 13 frigates with 10 new and upgraded ones. According to reports, this would effectively double Greece’s defence procurement budget to a billion euros a year.

October 2: Europe says it will reconsider sanctions, Turkey says it will occupy Varosha

The European Council called on Turkey to negotiate a continental shelf delimitation with Greece. It offered sticks and carrots – sanctions if Turkey fails to comply, versus customs union if it proceeds. The council said it would reconsider sanctions against Turkey by December.

On the same day, Erdogan announced that Turkey will occupy Varosha (Famagusta), the ghost town in eastern Cyprus Turkish troops seized in August 1974, which the UN repeatedly ordered them to return to the Republic of Cyprus (UNSCR 365, 367, 541, 544, 550).

October 15: Russia wades in, sides with Greece

Russia announced it was reversing its policy on the Aegean, and looked favourably on Greece extending its territorial waters off its islands there to 12 nautical miles. Such a move would allow Greece to control more than 70 percent of the Aegean. Russia also called on Turkey to delimit its EEZ with Greece in accordance with international law.

October 25: Greece, US ties appear strengthened

Greek Foreign Minister Nikos Dendias told parliament that Greece and the US are about to begin “almost immediately a new dialogue for the broadening of the Mutual Defence Co-operation Agreement or to reach an entirely new agreement”.

November 18: Greece, UAE sign strategic alliance

Greece and the UAE signed a strategic alliance in Abu Dhabi, which includes cooperation in the areas of the economy, tourism and defence.

December 10-11: European summit does not sanction Turkey

The European summit does not levy sanctions on Turkey, disappointing Greece and Cyprus, and postponing the issue until March.

December 14: US sanctions Turkey

The United States Congress passed sanctions against the Presidency of Turkish Defence Industries, an arm of the defence ministry, overriding a presidential veto from Donald Trump.