Syria has apologized through the United Nations for the mortar strike which killed five civilians in southeast Turkey on Wednesday and said such an incident would not be repeated, Deputy Prime Minister Besir Atalay said on Thursday.

"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.

The cross-border tensions escalated on Wednesday after a shell fired from inside Syria landed on a home in the Turkish village of Akcakale, killing a woman, her three daughters and another woman, and wounding at least 10 others, according to Turkish media.

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 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.

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, after a mortar bomb fired from the area killed five Turkish civilians.

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 U.S.-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.

"I want and hope that the entire international community, in particular through the Security Council, passes a clear and swift message that condemns the Syrian authorities strongly," French Foreign Minister Laurent Fabius said in a statement.

While Security Council 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.

The U.S. State Department said on Thursday it regarded Turkey's response to Syrian mortar fire as appropriate, proportionate and designed to deter any future violations of its sovereignty by Syria.

The department also believes Turkey, which has carried out retaliatory artillery strikes on a Syrian border town, has responded to Wednesday's mortar fire and that its parliament's actions were aimed at any future violations of its sovereignty, State Department spokeswoman Victoria Nuland told reporters.

Egypt and the Arab League speak out

Egypt and the Cairo-based Arab League meanwhile criticized Syria on Thursday for a mortar bomb that landed in Turkey, killing civilians and provoking a military response, saying the incident could endanger the whole region.

Egyptian Foreign Minister Mohamed Kamal Amr said Syria should stop bloodshed on its own soil and called on it not to "violate the borders of neighboring states," warning of the "numerous dangers to the whole region" if the crisis spread.

Arab League chief Nabil Elaraby offered condolences to Turkey over the mortar bomb which he said was "a serious threat to the peace and security in the region."