Turkey is to convene an emergency session of Nato after declaring that Syria's shooting down of one its fighter-jets amounted to a direct challenge to its national security.
The Turkish government brushed off protestations in Damascus that Friday's incident was an accident, accusing Syria of deliberately bringing down the F-4 Phantom both in international airspace and without warning.
Bringing a potentially dangerous international dimension to the stand-off, Turkey took the highly unusual step of invoking Article IV of Nato's founding charter as it sought Western backing for whatever response it chooses to make.
Article IV allows a Nato member to call for an emergency meeting of the whole alliance if it feels that its "territorial integrity, political independence or security" has been threatened. It has only been invoked once before, when Turkey, fearing a backlash by Saddam Hussein, successfully petitioned the alliance to station anti-missile batteries on its soil in the weeks before the US-led invasion of Iraq in 2003.
Nato said its governing body would meet on Tuesday to discuss how to respond.
Underlining Turkish anger, Ahmet Davutoglu, the country's foreign minister also said that a formal protest would be lodged with the United Nations Security Council.
Turkey's robust response was welcomed by Britain and some of its European allies. William Hague, the Foreign Secretary, described the incident as "outrageous" and warned Syria that it would face serious consequences.
"The Assad regime should not make the mistake of believing that it can act with impunity," he said. "It will be held to account for its behaviour. The UK stands ready to pursue robust action at the United Nations Security Council."
European Union foreign ministers, who will meet on Monday to discuss the incident, were similarly direct in the criticism of Syria. Giulio Terzi, Italy's foreign minister, said the shooting down of the jet was a "further extremely serious and unacceptable action by the Assad regime."
But there were calls for caution too, with Guido Westerwelle, the German foreign minister, saying: "Everything must be done to ensure that there won't be any further escalation in the already tense region."
Turkey has not yet revealed what measures it will take against Syria, nor what role Nato should play in them.
Diplomats suggested that Turkey would be more likely to seek political backing from Nato allies for whatever diplomatic or military steps it chooses to take.
There has been no suggestion that Turkey would invoke Article V of the Nato charter, which states that an attack on one member should be regarded as an attack on all, and could lead to military action by the entire alliance. The United States remains the only country to invoke the clause, doing so the day after the 9/11 attacks and paving the way for the Nato mission in Afghanistan.
Any attempt by Turkey to follow suit, even if it wanted to, would struggle to win UN legitimacy because Syria could mount an argument that it acted in self-defence.
The details of the incident remain in dispute. Turkey admitted that the aircraft had briefly and inadvertently entered Syrian territory. But Mr Davutoglu said the plane was shot down in international airspace and accused Syria of breaking all conventions over how to respond to an encroachment of his territory.
Syria neither made any attempt to communicate with the Turkish fighter, nor did it scramble its own air force, he said.
"According to our conclusions, our plane was shot down in international airspace, 13 nautical miles from Syria," he said.
"The plane did not show any sign of hostility towards Syria and was shot down about 15 minutes after having momentarily violated Syrian airspace.
"The Syrians knew full well that it was a Turkish military plane and the nature of its mission."
But Syria insisted that it had acted within its rights, and denied accusations that it had seen Turkish markings on the fighter.
"What happened was an accident and not an assault as some like to say, because the plane was shot while it was in the Syrian airspace and flew over Syrian territorial waters," said Jihad Makdissi, the Syrian foreign ministry's spokesman.
Turkey said the wreckage of the plane had been identified - within Syrian waters - but that it lay thousands of feet below the surface of the sea. Both pilots are still missing, raising public anger in Turkey.
Whatever the truth of the case, the incident will give Western powers greater justification to pursue Syria through the Security Council. Russia has twice blocked resolutions seeking to impose sanctions on the Assad regime, but has conspicuously refrained from making any official comment about Friday's incident.
Turkey could also use the loss of its fighter to renew its case for the imposition of an internationally-policed buffer zone in Syrian territories along the border.
Western powers toyed with the idea in the past, but chose instead to support a UN-backed ceasefire plan brokered by Kofi Annan, the international envoy to Syria.
But with that plan considered to have failed after a surge of violence in Syria, Western states are looking for alternatives and could be persuaded to back the Turkish idea, analysts said.