The Pentagon urged Russia and Turkey to de-accelerate the mounting tensions between the two countries following the downing of a Russian Fighter plane on the Syrian, Turkish border Tuesday, according to Reuters.

NATO Secretary General Jens Stoltenberg in a press statement made in Brussels, backs Turkey’s version stating that an allied assessment shows the Russian warplane did fly into Turkish airspace.

The circumstances that led to this are in dispute. Both Turkey and Russia claim to have proof of their account.  Turkish military has presented a map and the radar locations of the Russian fighter when the missiles were fired.

According to the BBC, the Turkish military said two F-16s on patrol had fired on an unidentified aircraft at 09:24 (07:24 GMT) after warning it 10 times over five minutes about violating Turkish airspace over the town of Yayladagi, in Hatay province.

In a report to Reuters, Russian President Vladimir Putin said the plane had been attacked when it was 1 kilometer inside Syria and warned of “serious consequences” for what he termed a stab in the back administered by “the accomplices of terrorists”.

“We will never tolerate such crimes like the one committed today,” Putin said, as Russian and Turkish shares fell on fears of an escalation between the two countries.

Footage from Turkey’s Anadolu Agency showed two pilots parachuting out of the jet before crashing.  A commander of the rebel Turkmen forces in Syria claimed to have shot both pilots dead as they came down. CNN reports that the body of one pilot has been found.

The BBC  reported that Russian aircraft have flown hundreds of sorties over northern Syria since September. Moscow says they have targeted only “terrorists”, but activists say its strikes have mainly hit Western-backed rebel groups.

Turkey, a vehement opponent of Syria’s president, has strongly cautioned against violations of its airspace by Russian and Syrian aircraft.

The Turkish foreign ministry warned the Russian ambassador last week that there would be “serious consequences” if the Russian air force did not immediately stop bombing “civilian Turkmen villages” in the Bayir Bucak area, near Tuesday’s crash site.