WASHINGTON (Reuters) - The United States expressed hope on Thursday that Turkey's border clash with Syria does not escalate further, but stood by its NATO ally's right to defend itself against aggression spilling over from Syria's internal armed conflict.
The State Department said Turkey's decision to mount retaliatory artillery strikes after a Syrian mortar killed five civilians in southeastern Turkey on Wednesday was appropriate and proportional.
Pentagon spokesman George Little told reporters, "We hope that this doesn't escalate into a broader conflict. We hope that the situation de-escalates."
Little added that the United States put the blame on Syrian President Bashar al-Assad's government. "We are outraged by the Syrian government's actions along the Turkish border. We stand with our Turkish allies," Little added.
Turkey stepped up retaliatory artillery strikes on a Syrian border town on Thursday, killing several Syrian soldiers, while its parliament approved further military action in the event of further spillover from the Syrian fighting.
"Our understanding is that the Turks have responded. The Turkish Parliament has also given the government the capacity to respond again if there are future such violations of Turkish sovereignty," State Department spokeswoman Victoria Nuland said.
"From our perspective, the response that Turkey made was appropriate, it also was designed to strengthen the deterrent effect so that these kinds of things don't happen again, and it was proportional," Nuland told reporters.
Syria apologized through the United Nations on Thursday for the mortar fire and said it would not happen again, Turkey's Deputy Prime Minister Besir Atalay said.
The attack was the most serious escalation of tensions between the two neighbors since Syrian forces shot down a Turkish fighter jet in June. It highlighted the rising risks of a broader conflict as Assad's 18-month crackdown on armed rebels continues.
The United States joined other NATO members in voicing solidarity with Turkey after Ankara requested an emergency late-night meeting to discuss the strike.
While the U.S.-led Western military alliance called on Syria to put an end to "flagrant violations of international law," political analysts see little appetite in either the United States or NATO for more aggressive action right now.
"Turkey's allies, beginning with the United States, are rhetorically committed to Assad's overthrow, but are not committed to the additional steps that Turkey would like to see," said Bulent Aliriza, director of the Turkey Project at the Center for Strategic and International Studies think tank in Washington.
"The likelihood of Turkey sending troops across the border in large numbers seems extremely low," Aliriza added. "Turkey finds itself, despite all the words of support, isolated and under pressure."
U.S. officials have underscored that Turkey is a key partner as they seek to muster a coordinated international response to Syria's crisis, which has transformed from an anti-government uprising into a sectarian conflict that analysts say could destabilize neighboring states.
Secretary of State Hillary Clinton spoke with her Turkish counterpart, Ahmet Davutoglu, on Wednesday and pledged U.S. support for Turkey both in NATO and at the U.N. Security Council, where Assad's chief ally Russia sought to water down a proposed statement condemning the attack.
The Pentagon said that Defense Secretary Leon Panetta has not been in touch with Turkish officials, and neither has the top U.S. military officer, General Martin Dempsey. That could suggest that the United States is not girding for broader military fallout from the border shelling incident.
"The secretary has not had any contact with Turkish officials, but certainly we respect the inherent right of self-defense displayed by Turkey," Little said.
Henri Barkey, a Turkey expert at Lehigh University in Pennsylvania, said the measured U.S. response is a signal to Turkey to stay the course on Syria - although this could prove increasingly difficult if the violence continues to spread across the two countries' 566-mile border.
"This incident, if it were to be repeated in the future, is only going to increase Turkey's demands on us. They are going to say, 'We are being attacked and our allies are doing nothing for us,'" Barkey said.
"I think all of us, not just the Turks, are going to have to come up with a new policy that takes into account that this civil war in Syria may last another year or so. All of us are going to have to adapt," Barkey added.
Additional reporting By Arshad Mohammed; Editing by Will Dunham