Turkey's parliament gave authorization on Thursday for military operations outside Turkish borders if the government deemed them necessary, a day after artillery shelling from Syria killed five civilians in a Turkish border town.

The government had sought parliamentary approval to send soldiers to foreign countries in a memorandum which said that "aggressive action" by Syria's armed forces against Turkish territory posed a serious threat to national security.

After the Turkish parliament gave its authorization, Turkish Deputy Prime Minister Besir Atalay clarified that Ankara's priority is to act in coordination with international institutions.

Speaking to reporters after parliament authorized military operations outside Turkish borders if the government deemed them necessary, Atalay said Turkey had exercised its right to retaliation and that the assembly's authorization was not a "war memorandum."

Thursday afternoon Turkish Deputy Prime Minister Besir Atalay said that Syria has apologized through the United Nations.

"Syria accepts that it did it and apologizes. They said nothing like this will happen again. That's good. The UN mediated and spoke to Syria in the evening," Atalay said.

Earlier Thursday, European Union foreign policy chief Catherine Ashton condemned the mortar strike but called for restraint from all sides.

"I strongly condemn yesterday's shelling by Syrian forces of the Turkish border town," she said in a statement. "I once again urge the Syrian authorities to put an immediate end to the violence and fully respect the territorial integrity and sovereignty of all neighboring countries."

Turkey has retaliated against the attack, hitting targets nears Syria's Tel Abyad border but Ashton said violence should stop.

"I call for restraint from all sides and will continue to follow the situation extremely closely," she said.

British Foreign Secretary William Hague also issued a warning on Thursday, telling Reuters that Turkey's military response was understandable, but an escalation of the situation should be avoided.

"The Turkish response is understandable, an outrageous act has taken place, Turkish citizens have been killed inside Turkey by forces from another country," Hague said. "So we express our strong solidarity with Turkey but we don't want to see a continuing escalation of this incident."

Hague said the Syrian government should make sure that "there is no repetition whatever of any incident of this kind so that such tensions on border regions with Turkey or with other neighboring countries can be avoided."

Turkish artillery hit targets near Syria's Tel Abyad border town for a second day on Thursday, killing several Syrian soldiers according to activists and security sources.

Turkey's government said "aggressive action" against its territory by Syria's military had become a serious threat to its national security and sought parliamentary approval for the deployment of Turkish troops beyond its borders.

"Turkey has no interest in a war with Syria. But Turkey is capable of protecting its borders and will retaliate when necessary," Ibrahim Kalin, a senior adviser to Turkish Prime Minister Tayyip Erdogan, said on his Twitter account.

"Political, diplomatic initiatives will continue," he said.

In the most serious cross-border escalation of the 18-month uprising in Syria, Turkey hit back after what it called "the last straw" when a mortar hit a residential neighborhood of the southern border town of Akcakale on Wednesday.

The Syrian Observatory for Human Rights said several Syrian soldiers were killed in the Turkish bombardment of a military post near the Syrian town of Tel Abyad, a few miles across the frontier from Akcakale. It did not say how many soldiers died.

"We know that they have suffered losses," a Turkish security source told Reuters, without giving further details.

NATO said it stood by member-nation Turkey and urged Syria to put an end to "flagrant violations of international law."

The US-led Western military alliance held an urgent late night meeting in Brussels to discuss the matter and in New York, Turkey asked the UN Security Council to take the "necessary action" to stop Syrian aggression.

In a letter to the president of the 15-nation Security Council, Turkish UN Ambassador Ertugrul Apakan called the firing of the mortar bomb "a breach of international peace and security."

UN diplomats said Security Council members hoped it would issue a non-binding statement on Thursday that would condemn the mortar attack "in the strongest terms" and demand an end to violations of Turkey's territorial sovereignty.

Members had hoped to issue the statement on Wednesday, but Russia - a staunch ally of Syria's, which along with China has vetoed three UN resolutions condemning President Bashar Assad's government - asked for a delay, diplomats said.

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