By Adam Levine, CNN
Turkey's leadership took on a much more strident tone on Sunday, calling the downing of its military jet by Syria an "act of aggression" and invoking its right to consult with other NATO nations. That call to meet has raised the question of whether other nations, including the United States, would be compelled to strike back on Turkey's behalf.
Turkish Foreign Minister Ahmet Davutoglu has spoken with U.N. Secretary-General Ban Ki-moon, the foreign ministers of the United States, the United Kingdom, France, Russia and Iran, and European Union foreign policy chief Catherine Ashton since the incident, spokesman Selcuk Unal told CNN Saturday.
British Foreign Minister William Hague Sunday called the incident "outrageous" and said he condemned it wholeheartedly."
"The Assad regime should not make the mistake of believing that it can act with impunity. It will be held to account for its behavior," Hague said of Syrian President Bashar al-Assad.
The top American military official, chairman of the Joint Chiefs of Staff Gen. Martin Dempsey, called his Turkish counterpart this weekend, a U.S. official told CNN's Barbara Starr.
Secretary of State Hillary Clinton spoke with her Turkish counterpart, as well. In a statement issued Sunday she called the incident a "brazen and unacceptable act in the strongest possible terms."
NATO members will be meeting this Tuesday in Belgium to discuss the incident, at the request of Turkish officials, according to NATO spokeswoman Oana Lungescu.
The meeting, or "consultations," is one Turkey called under Article 4 of the NATO treaty, Lungescu said in an e-mail to CNN. Turkey is expected to make a presentation about the plane incident.
"Under Article 4, any ally can request consultations whenever, in the opinion of any of them, their territorial integrity, political independence or security is threatened," she wrote.
With the consultations, there is a chance Turkey will demand a collective military response. The notion comes from what is known as Article 5 of the North Atlantic Treaty Organization's Washington Treaty, which states that should a member nation - which Turkey is - be attacked, other NATO members are compelled in a collective act of self-defense "such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area."
Article 5 has been invoked just once since NATO's founding, the military response to 9/11.
In this incident, after restrained comments early on, Turkey has issued much angrier comments as details became known. On Sunday, Turkey's foreign minister said the country will act "decisively" within international law and refuted Syria's contention that the plane was shot down because it displayed an "act of aggression."
The plane in the Friday incident was unarmed and sending no hostile signals, said Davutoglu. The plane was testing Turkey's radar systems, Davutoglu said.
"You have to first send a caution, a warning," he said in the first detailed Turkish statement on the international incident. "If the warning doesn't work, you scramble your planes, you send a stronger signal, you force the plane to land. There wasn't enough time to do any of that in the time that our plane was in Syrian airspace."
Davutoglu added the plane was shot down in international air space.
Turkey has invoked Article 4 before, after tensions arose on its border with Iraq.
"This did not lead to the invocation of Article 5," Longescu noted.
A senior American administration official speaking on background because of the sensitivity of the issue, told CNN's Jill Dougherty on Sunday that Turkey's request "is just consultations, and they aren't asking for more than that." The official added that the move does mean Turkey considers Syria's shooting down their plane a threat to Turkey's security.
If NATO was looking for a fight, this would be a good opportuity to invoke Article 5, but there is no appetite for a military conflict with Syria at the moment, several NATO diplomats told CNN's Elise Labott on Sunday.
There are many factors that weigh against a military response. First and foremost, the North Atlantic Council has to agree to it. Also, even if agreed, each member can contribute as they see fit.
"This is an individual obligation on each Ally and each Ally is responsible for determining what it deems necessary in these particular circumstances," according to a description of the charter posted on the NATO website.
The United States and many other countries have been vocally opposed to military intervention and will not be quick to encourage Turkey to press the issue. After Syrian troops shelled refugees on the Turkish side of the border earlier this year, Secretary of Defense Leon Panetta made clear that the bar was high for Turkey to claim the need for a collective self-defense.
Panetta was asked about invoking Article 5 at a House Armed Services Committee hearing in April.
"I think it's clear that the only way that the United States would get involved militarily is if there's a consensus in the international community to try to do something along those lines. And then obviously ensure that the international community is able to get the - the authorities required in order to make that happen," Panetta said. "They would have to make clear that what is happening there really does truly represent a direct threat to Turkey. And I think at this point, that's probably a stretch."
In her statement Sunday, Clinton said the U.S. would keep in contact with Turkey as the country determines its response. The U.S. will "work with Turkey and other partners to hold the Assad regime accountable," Clinton said.
NATO members agreeing to respond to this incident is "inconceivable," wrote James Joyner on the Atlantic Council blog. Joyner, who said he opposes military intervention in Syria, felt the incident does not rise to the level of such a response.
"The operative word that almost certainly disqualifies this incident from an Article 5 response is 'attack.' Turkey was engaged in aggressive action along its border with Syria during a particularly tense situation and flew into Syrian airspace," Joyner wrote on Friday, "While shooting down the plane was almost certainly an overreaction - the Assad government has said as much - it's hardly an 'attack.'"
Additionally, Joyner said, the article demands response "to restore and maintain the security of the North Atlantic area."
"Given that the incident is already contained - that is, not likely to be followed by any sort of follow-on action by Syria absent further provocation - said security already exists. Indeed, a NATO or Turkish response would make the area more, not less, secure," Joyner maintained.
But Turkey's prime minister, Recep Tayyip Erdogan, may feel compelled to make a decisive response, said Hoover Institution's Fouad Ajami, who explained Erdogan is already under pressure after he turned against Syria's regime and called for the rescue of the Syrian people.
"I think it would be an embarrassment to Prime Minister Erdogan, because he has to make good on the threats that he has made," Ajami said in an interview with CNN's Candy Crowley broadcast on "John King, USA."
Ajami said the shootdown is a worrisome development as it demonstrates Syrian president al-Assad's "sense of abandon."
"Turkey is a NATO member. Turkey is a very, very formidable power. Turkey is four times the size of Syria. The Turkish military is a mighty institution.
"And the idea that this ragtag regime in Damascus would shoot down a Turkish airplane, a jet fighter ... a Phantom - F-4 Phantom plane - tells you that Bashar al-Assad's regime has the sense of invulnerability, that no one is coming to the rescue of the Syrian population," Ajami said on Friday.
But in the end, nobody is expecting the Turks even to ask to invoke Article 5, knowing that NATO would probably not go along, diplomats told CNN on Sunday. The impression was that Turkey itself does not want to ratchet thing up that high, either.