Turkey says that after issuing 10 warnings in five minutes, two of its F-16s shot down a Russian warplane that Turkey claims violated its airspace.
On Twitter, Russia's Defense Ministry said its Sukhoi SU-24 was flying "only within the borders of Syrian territory." Its pilots, the Russians said, appear to have ejected.
Later in the day, Russian President Vladimir Putin called the action a "stab in the back by the terrorists' accomplices."
According to The Associated Press, Putin went on to say that there would be "significant consequences."
"We will never tolerate such atrocities as happened today and we hope that the international community will find the strength to join forces and fight this evil," Putin said.
The AP published video that appears to show a damaged warplane crash into a hillside. The video, shot from Turkey's Hatay province, then appears to show the pilots parachuting down:
The Washington Post reports that Russia initially disputed Turkey's version of events, saying the plane was likely downed "due to shelling from the ground."
"The incident highlights heightened friction in Syria's increasingly crowded airspace, which now includes Russian warplanes that are targeting the armed opposition of President Bashar al-Assad's embattled forces.
"Russian President Vladimir Putin's spokesman called the warplane's downing a 'very serious incident,' but said it was too early to draw conclusions.
" 'It is just impossible to say something without having full information,' Dmitry Peskov, Putin's spokesman, told reporters in Moscow. While Peskov urged caution, however, some Russian lawmakers called for retaliation against Turkey by evacuating Russian tourists from popular vacation destinations there."
"The Dogan news agency said that witnesses said the warplane crashed over tents in a village and pilots landed with parachutes. Russia's Interfax agency said the pilots ejected, and what happened to them is under investigation, citing the defense ministry."