ISTANBUL -- With the backing of the NATO alliance, which unanimously condemned Syria for shooting down an unarmed Turkish reconnaissance plane last week, Turkey warned Tuesday that its military will be prepared to attack any Syrian military element that crossed their common border.

Turkey’s wrath is “strong and devastating,” Prime Minister Recep Tayyip Erdogan said in a speech to legislators of his Justice and Development Party in which he announced new rules of engagement for the military.

“Every military element approaching Turkey from the Syrian border and representing a security risk and danger will be assessed as a military threat and will be treated as a military target,” he said.

In Washington, an Obama administration official declined to discuss the details of the downing of the Turkish aircraft other than to say it confirmed a U.S. belief, voiced in briefings earlier this year, that Syria’s air-defense system is “robust” and would pose "an extraordinary challenge." to Western militaries if they attempted to impose a no-fly zone over the country. In those briefings, officials said the Syrian air defense system included surface-to-air missiles as well as more traditional anti-aircraft weapons and 500 military aircraft. The official spoke under a condition of anonymity imposed at the time of the original briefing.

Erdogan said five Syrian helicopters had made incursions into Turkish territory in the past year, but they were peacefully warned to leave.

From this point on, “There’s no more Mr. Nice Guy,” Selcuk Unal, the spokesman for the Foreign Ministry, told McClatchy.

Despite the open warning, Turkey has taken care not to escalate Friday’s shoot-down of the U.S.-built F-4 Phantom into a military confrontation, and key Western allies have expressed relief at Turkey’s restraint.

Moreover, Erdogan’s remarks made clear that the Turkish military would act only after weighing “the security risk,” a step the Syrian government admitted it had failed to do when its forces shot down the plane. Or, as the Turkish ministry spokesman put it, “We reserve our right to take the necessary steps at a time and method of our choosing.”

Still, the Turkish rhetoric was several notches more emotional Tuesday than it had in previous days, possibly a reaction to what the government in Ankara views as an unacceptable response by the autocratic government of Syrian President Bashar Assad. Erdogan said the Assad regime, which has deployed all its military and intelligence forces to fight a nationwide pro-democracy insurrection, didn’t represent the Syrian people.

“The current Syrian administration is a tyrannical regime that murders its own people,” Erdogan said, adding that Assad’s regime “has lost all legitimacy.”

Syria “already has become an unstable threat in Turkey’s neighborhood,” the Foreign Ministry spokesman said.

Turkish officials say Syria attacked the plane without warning, lied about the incident and then failed to apologize.

Syria claimed it brought down the plane over its airspace using an automatic anti-aircraft system without knowing that it was Turkish. Turkey said Syria brought down the plane over international waters – 15 minutes after the aircraft had crossed inadvertently into Syrian airspace – and that radio intercepts proved the Syrians knew the plane was Turkish.