Washington — State Department spokeswoman Victoria Nuland says Turkey's response to a recent mortar attack on civilians from Syrian military forces was appropriate and proportional.

At a State Department briefing October 4, Nuland told journalists that “as was clear last night in the unanimous support that Turkey had from the North Atlantic Council, from our perspective, the response that Turkey made was appropriate.” The North Atlantic Council is the ruling body of NATO, of which Turkey is a member.

Nuland said the Turkish response was designed “to strengthen the deterrent effect that these kinds of things don’t happen again, and it was proportional.”

Syrian military forces fired mortar rounds into Turkey on October 3, killing at least five Turkish citizens. Later the same day, Turkey responded with artillery fire on targets in Syria.

Nuland said Secretary of State Hillary Rodham Clinton told Turkish Foreign Minister Ahmet Davutoğlu by telephone that the United States extended its deepest condolences to the families of the Turkish victims killed and those injured by the mortar attack from Syria.

“The secretary also used that opportunity to condemn the Syrian attack and to pledge U.S. support for our ally Turkey,” Nuland told journalists.

Nuland also said the United States has no reason to challenge the Turkish military and the government’s assertions that the mortar attack was fired by the Syrian military. She noted that, since the attack, the Syrian regime has acknowledged the attack and apologized to Turkey.

“Our fervent hope and expectation is that there will not be further violations of Turkish sovereignty,” Nuland said.

NATO issued a statement in Brussels following an emergency session condemning the Syrian attack.

NATO officials said in the statement that “in view of the Syrian regime’s recent aggressive acts at NATO’s southeastern border, which are a flagrant breach of international law and a clear and present danger to the security of one of its allies, the North Atlantic Council met today [October 3], within the framework of Article 4 of the Washington Treaty, and discussed the continuous shelling of locations in Turkey adjacent to the Turkish-Syrian border by the Syrian regime forces.”

“The most recent shelling on 3 October 2012, which caused the death of five Turkish citizens and injured many, constitutes a cause of greatest concern for, and is strongly condemned by, all allies,” the statement says.

“In the spirit of indivisibility of security and solidarity deriving from the Washington Treaty, the alliance continues to stand by Turkey and demands the immediate cessation of such aggressive acts against an ally, and urges the Syrian regime to put an end to flagrant violations of international law,” it says.

U.S. Permanent Representative to the United Nations Susan Rice told journalists in New York October 4 that the United States strongly condemned the shelling.

“Turkey is a core ally of the United States, and this sort of cross-border military activity is very destabilizing and must be stopped,” Rice said.

A spokesman for U.N. Secretary-General Ban Ki-moon said Ban “is alarmed by escalating tensions along the Syrian-Turkish border.”

Ban's spokesman, Martin Nesirky, told journalists October 4 at U.N. headquarters that “as the situation inside Syria deteriorates yet further ... the risks of regional conflict and the threat to international peace and security are also increasing.”

Turkey asked the U.N. Security Council to take the “necessary action” to stop Syrian aggression and ensure Turkish territorial integrity is respected.

Turkey's parliament gave authorization on October 4 for military operations outside Turkish borders, if the government deemed them necessary.