The head of the NATO military alliance has described the downing of a Turkish fighter jet by Syrian government forces unacceptable.

The condemnation came shortly after Turkey briefed NATO's North Atlantic Council in discussions on Tuesday held under Article 4 of NATO's founding treaty, which allows a NATO member to request consultations if its security has been threatened.

Anders Fogh Rasmussen, NATO's secretary-general, said the alliance condemned it "in the strongest terms", and expressed solidarity with Turkey, but made no mention of retaliatory action.

For his part, Turkey's prime minister, responding to the incident in a speech to the ruling AK party's parliamentary group, said the Turkish military will respond to any future violation of its border by the Syrian military.

"The rules of engagement of the Turkish Armed Forces have changed," Recep Tayyip Erdogan said.

"Any military element that approaches the Turkish border from Syria by posing a security risk and danger will be regarded as a threat and treated as a military target."

Conflicting claims

Syria insists that the Turkish aircraft violated its airspace on Friday.

But Turkey says that although the unarmed RF-4E reconnaissance jet had unintentionally strayed into Syria's air space, it was inside international airspace when it was brought down.

Erdogan said Syria shot down the unarmed plane in international airspace in a "deliberate" and "hostile" act and without warning.

He said border violations in the region were not uncommon, and claimed that Syrian helicopters violated Turkish airspace five times recently, without Turkish response.

"The Syrian regime has no more legitimacy, that is clear. Women, children, the elderly, have been killed relentlessly by this tyranny," Erdogan said.

"No one should be deceived by our cold blooded stance," he said. "Our acting with common sense should not be perceived as a weakness."

But Russia, one of Syria's closest allies, said on Tuesday that the incident should not be seen as a provocation.

"It is important that what happened is not viewed as a provocation or a premeditated action," the foreign ministry said in a statement on its website, which went on to call for restraint.

Al Jazeera's Rula Amin, reporting from Beirut, said that by shooting down the Turkish jet, the Syrians had successfully marked the limits of foreign intervention in their affairs.

"For the Syrians, they have made their point," she said.

"They are not going to tolerate any violations of their airspace … What they're saying is that they're still strong, they are defiant, and they will fight back."

The downing of the jet has aggravated tense ties between the two neighbours.

'Violent and crushing'

Turkey has repeatedly called on Syrian President Bashar Assad to step down as 33,000 Syrians have sought refuge on its soil, fleeing a government crackdown on a popular uprising.

Erdogan said as much as Turkey's friendship is valuable, Turkey's "wrath is as much violent and crushing".

He said: "we will continue to be a burning torment for circles who have adopted a hostile attitude towards Turkey."

Al Jazeera's Anita McNaught, reporting from Ankara, said that Syria's decision to shoot down the plane came after months of what Damascus regarded as Turkish meddling in its internal affairs.

The fact that the rebel group, the Free Syrian Army, is increasingly using Turkey as the base from which it conducts operations against the Syrian government has antagonised the Assad government, she said, as has its belief that Turkey is now turning a blind eye to weapons being smuggled into Syria.

"Turkey does believe that it stood strongly besides Syria, and gave it the best advice in the world," our correspondent said.

Public anger in Turkey is largely muted, with Huseyin Celik, a senior member of the AKP, saying that the party's grass-roots is against going to war.