BEIRUT — Turkey’s parliament voted Thursday to authorize military cross-border operations into Syria, a day after an apparently errant mortar strike from inside Syria killed five Turkish civilians.

Deputy Prime Minister Besir Atalay told the Associated Press that the 320-129 vote “is not for war,” but is intended to deter Syria from further violence that could spill over the border.

Atalay also said that Syria has taken responsibility and formally apologized for the death of the five Turkish civilians, and reassured the United Nations that “such an incident will not occur again,” AP reported.

Though this was not the first time the Syrian conflict has spilled over into Turkey, the five people killed Wednesday after a shell launched by the Syrian military crashed into the Turkish border town of Akcakale were the first Turkish civilians to die.

Within hours of the strike, Turkey launched two artillery attacks against Syria in retaliation, marking the most serious escalation in international tensions since the Syrian revolt erupted 19 months ago.

“Our armed forces in the border region responded immediately to this abominable attack in line with their rules of engagement; targets were struck through artillery fire against places in Syria identified by radar,” said a statement issued by the office of Prime Minister Recep Tayyip Erdogan.

The British-based Syrian Observatory for Human Rights quoted activists in the Syrian border town of Tal Abyad as saying that an unspecified number of Syrian soldiers were killed by artillery fire that struck a military base Thursday morning.

Turkey has shown a willingness in the past to send troops into neighboring countries to address perceived threats to its safety. Specifically, it repeatedly sent forces into Iraq to combat Kurdish guerrillas who had struck at Turkish targets.

Amid growing international concerns that the conflict could escalate further, Syria’s ally Russia on Thursday urged Syria to publicly admit that its forces had fired the shell that killed the civilians.

Russian Foreign Minister Sergei Lavrov said the Syrian authorities had told him the incident “was a tragic accident and that it will not happen again,” the Russian news agency RIA quoted him as saying during a visit to Islamabad.

“We think it is of fundamental importance for Damascus to state that officially,” he added.

NATO, of which Turkey is a member, met in emergency session Wednesday at Turkey’s request and issued a strongly worded statement calling the Syrian shelling “a flagrant breach of international law and a clear and present danger to the security of one of its Allies.” Although NATO pledged to continue to “stand by Turkey,” it proposed no immediate action.

U.S. reaction

In Washington on Wednesday, the White House also condemned the Syrian shelling and affirmed the United States’ solidarity with Turkey. “We stand with our Turkish ally and are continuing to consult closely on the path forward,” National Security Council spokesman Tommy Vietor said.

Pentagon spokesman George Little condemned what he called “the depraved behavior of the Syrian regime.”