The White House on Monday promised to work with Turkey and other NATO allies to hold Syria "accountable" for what American officials have described as the deliberate downing of a Turkish military jet, apparently in international airspace.

Turkey said it would push NATO, whose governing body meets Tuesday to discuss the matter, to consider the June 22 incident an attack on the entire alliance. Under Article V of NATO's founding document, an attack on one member is considered an attack on all.

"We stand in solidarity with Turkey, a key U.S. ally," spokesman Jay Carney told reporters aboard Air Force One. "We will work with Turkey, and other partners, to hold the Assad regime accountable."

Carney indicated that Washington preferred a diplomatic resolution to the flare-up in tensions. "We obviously support the Turks and we'll work with them," he said. "Turkey is a key ally of the United States, member of NATO."

Military action is unlikely. NATO operates by consensus, meaning its members must all agree on a course of action. While there have been media reports that Washington has been helping to coordinate weapons shipments from other countries to Syria's rebels, the U.S. has denied arming the uprising, and there is little appetite among Americans for another war in the Middle East.

Still, President Barack Obama has expressed mounting frustration with the weak international response to Syrian President Bashar al-Assad's 15-month crackdown on opposition to his iron-fisted rule. Outside observers have put the death toll at around 14,000. Russia and China have blocked U.N. Security Council approval of tighter sanctions on Assad's regime. And the violence has eroded relations between Washington and Moscow.

Secretary of State Hillary Clinton denounced the shoot-down as a "brazen and unacceptable act" after discussing the incident by telephone with Turkish Foreign Minister Ahmet Davutoglu on Sunday.

"It is yet another reflection of the Syrian authorities' callous disregard for international norms, human life, and peace and security," Clinton said in a statement.

According to media reports, Turkey's government says its RF-4E reconnaissance jet was shot down inside international airspace and the two Turkish crews are still missing. The government in Ankara has admitted that the plane had strayed inside Syria for approximately five minutes, but that it had realized its error and was in international airspace when it was hit.