Smoke rises over the streets after an mortar bomb landed from Syria in the border village of Akcakale, southeastern Sanliurfa province.

Beirut -

The Turkish army launched an artillery strike on Syria in retaliation for a Syrian mortar attack, escalating tensions in the volatile region and triggering an emergency meeting of NATO.

The Syrian attack on Wednesday reportedly killed five people. Activists at the Syrian-Turkish border said by phone that Turkey struck military posts of the Syrian government in the Tal Abyad region.

The Syrian mortar attack targeted Akcakale in Turkey's Sanliurfa province. Activists in the area said at least five Syrian shells had landed. Turkish media, quoting government sources, reported that the victims were a mother and four of her children.

Turkey's retaliation later on Wednesday marked the first time it has fired into Syria during 19 months of conflict between Syrian government forces and rebels. Syrian forces shot down an Turkish Air Force RF-4 plane in June, but Ankara did not retaliate.

Syria would investigate the shelling, Information Minister Omran al-Subi said. He also expressed the Syrian government's condolences to relatives of the victims and the Turkish people, the state-run SANA news agency reported.

Turkey, a member of NATO, immediately after the shelling called for an emergency meeting of NATO ambassadors in Brussels under Article 4, which allows for consultations if a NATO member state feels its sovereignty is threatened.

The NATO ambassadors called on Syria to immediately end its “aggressive acts” against Turkey, pledging its full support to Ankara and demanding an immediate end to the aggression.

It also urged “the Syrian regime to put an end to flagrant violations of international law” as all of its members “strongly condemned” the Syrian shelling.

The alliance described the “Syrian regime's recent aggressive acts” on the borders of NATO's territory as “a flagrant breach of international law and a clear and present danger to the security of one of its allies.”

Turkey also turned to the UN Security Council, writing a letter asking the highest UN decision-making body to stop Syria's aggression.

Wednesday's attack was a violation of international law and a strike against international peace and security, the letter said, according to Turkish media reports.

In Washington, the White House emphasised its support for Turkey and condemned Syria for aggression against its NATO ally.

“We stand with our Turkish ally and are continuing to consult closely on the path forward,” said Tommy Vietor, spokesman for the National Security Council in the White House.

US Secretary of State Hillary Rodham Clinton said the US was outraged that the Syrians had shot across the border into Turkey.

“It's a very, very dangerous situation,” Clinton said.

Turkey's parliament was scheduled Thursday to debate legislation in a special session that would make intervention in Syria possible, Turkish media reports said.

The legislation was proposed in a nearly four-hour meeting that included Prime Minister Recep Tayyip Erdogan; Foreign Minister Ahmet Davutoglu; General Necdet Ozel, chief of the general staff; and Justice Minister Sadullah Ergin.

Similar legislation authorising “operations outside the Turkish borders” allowed military action against Kurdish extremists in northern Iraq.

The legislation said the crisis in Syria not only negatively influences stability in the region but also in increasing measure Turkey's national security.

In New York, the Turkish ambassador to the United Nations met with the president of the 15-nation Security Council, Guatemalan Ambassador Gert Rosenthal.

Davutoglu complained to UN Secretary General Ban Ki-moon about the mortar attack.

Ban “expressed his condolences at the tragic loss of life and encouraged the minister to keep open all channels of communication with the Syrian authorities with a view to lessening any tension that could build up as a result of the incident,” said Martin Nesirky, a spokesman for Ban.

Turkey is host to tens of thousands of Syrian refugees in camps along its border with Syria.

The cross-border attacks followed another bloody day in Syria, which included the killing of at least 31 people in Aleppo in three bombings in the heart of the city, state television reported. - Sapa-dpa