Russian Sukhoi Su-24 shootdown

US President Donald Trump and Turkish President Tayyip Erdogan in a phone call on Monday discussed a Turkish proposal to strike a joint working group on its planned purchase of a Russian S-400 missile defense system, the Turkish Presidency said.

Remarks late Thursday by Turkish President Recep Tayyip Erdogan that his country will respond every time Greek fighter jets fly over the Aegean were described by the Greek Foreign Ministry as "completely unacceptable" and part of a deliberate effort by Ankara to stoke tensions.

Turkey will never turn back from a deal to purchase S-400 missile defence systems from Russia, President Tayyip Erdogan said on Wednesday, adding that Ankara may subsequently look into buying S-500 systems.

A Turkish court on Feb. 26 acquitted a Syrian military pilot who was accused of espionage when he was captured in 2017 after his jet crashed in Turkey. 

President Recep Tayyip Erdoğan has turned down a call by the U.S. to scrap a deal to buy the Russian S-400 missile defense systems, saying Washington should not conflate the issue of Ankara's procurement of defense systems with the two NATO allies' cooperation in Syria.

Russia claimed that its S-300 defense system will be able to close parts of the Syrian airspace "where necessary", a Russian Foreign Ministry director said in a news conference on Tuesday.

President Recep Tayyip Erdoğan has criticized the recent decision by United States authorities to delay the delivery of the jets, saying "Turkey has alternatives other than F-35 fighter jets," after Ankara's purchase of S-400 missile defense systems from Russia caused further tensions.

Turkish defense minister and his Russian counterpart spoke over the phone about regional security, according to a Turkish ministerial source on Aug. 30.

Solidarity between Ankara and Moscow "makes someone jealous," Turkish President Recep Tayyip Erdoğan has said at a meeting with Russian counterpart Vladimir Putin in Johannesburg, on the sidelines of the ongoing BRICS summit.

Russian President Vladimir Putin said on May 25 that Turkey has the right to choose its own military aircraft, amid Ankara's deal to buy missile-defense systems from Russia.