Russia has warned of "significant consequences" after Turkish fighter jets shot down one its warplanes.
Ankara said its F-16s shot down the Russian plane after it violated Turkish air space and ignored repeated warnings.
Nato is holding an emergency session in response to the incident, thought to be the first time one of the alliance's planes has shot down a Russian aircraft in half a century.
Moscow at first claimed the Su-24 jet was shot down by rebels opposed to Syrian president Bashad Assad, but later confirmed it was targeted by a Turkish F-16.
Russian president Vladimir Putin warned of "significant consequences for Russian-Turkish relations".
He said: "Our aircraft was shot down over Syrian territory by an air-to-air missile launched from a Turkish F-16 plane.
"It fell on Syrian territory, four kilometres from the Turkish border. When it was attacked in the air, it was flying at an altitude of 6,000 metres, one kilometre away from the Turkish territory. In any case, our plane and our pilots were in no way a threat to the Turkish Republic in any way. This is obvious."
Mr Putin claimed the Russian plane was involved in the effort to target Islamic State (IS) militants and accused Turkey of trading with the jihadist group, which is also known as Isil, Isis and Daesh.
He said: "We have long been recording the movement of a large amount of oil and petroleum products to Turkey from Isis-occupied territories. This explains the significant funding the terrorists are receiving.
"Now they are stabbing us in the back by hitting our planes that are fighting terrorism."
Russian foreign minister Sergey Lavrov cancelled a visit to Turkey planned for Wednesday.
Turkish prime minister Ahmet Davutoglu insisted his country has the right to take "all kinds of measures" against violations of its air space, and called on the international community to work towards "extinguishing the fire that is burning in Syria".
At Westminster, Foreign Secretary Philip Hammond told MPs that officials were urgently seeking details about the incident from Ankara and Moscow.
Updating MPs, Mr Hammond chose his words carefully, saying the jet was shot down "near the Turkish-Syrian border".
He said: "We are seeking further details urgently, both in Moscow and in Ankara. Clearly this is potentially a serious incident, but it wouldn't be wise to comment any further until we have got more certainty on the facts."
Nato was holding an extraordinary meeting of its main decision-making body the North Atlantic Council in Brussels at the request of Turkey.
"The aim of this extraordinary NAC meeting is for Turkey to inform allies about the downing of a Russian airplane," spokeswoman Carmen Romero said.
"Nato is monitoring the situation closely. We are in close contact with Turkish authorities."
Video footage of the incident showed a plane on fire before crashing on a hill and two crew members apparently ejecting.
Jahed Ahmad, of the 10th Brigade in the Coast, said the crew members tried to land with their parachutes in Syrian government-held areas after they ejected, but came under fire from members of his group.
He added that rebels shot one of the pilots, who landed dead on the ground. The fate of the second pilot was not immediately known.
The incident comes as David Cameron prepares to make the case for RAF air strikes in Syria.
The Prime Minister will set out a plan on Thursday to tackle IS in its Syrian stronghold.
He told the Commons on Monday that he would let MPs consider his proposals over the weekend before a debate and vote on British military involvement in Syria.
"I do not want anyone to feel that they are being bounced into a decision," he said. "I want this House to take the decision deliberately, but we should not take too long over it."