Prime Minister Tayyip Erdogan
Turkish artillery hit targets inside Syria on Wednesday after a mortar bomb fired from Syrian territory killed five Turkish civilians, while NATO called for an immediate end to Syria's "aggressive acts".
In the most serious cross-border escalation of the 18-month uprising in Syria, Turkey hit back at what it called "the last straw" when a mortar hit a residential neighbourhood of the southern border town of Akcakale.
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 later on Tuesday in New York, Turkey asked the U.N. Security Council to take the "necessary action" to stop Syrian aggression, reports Reuters.
In a letter to the president of the 15-nation Security Council, Turkish U.N. Ambassador Ertugrul Apakan called the firing of the mortar bomb "a flagrant violation of international law as well as a breach of international peace and security."
There were no immediate details of the Turkish strikes against Syria, nor was it clear who had fired the mortar into Turkish territory, but security sources said Turkey was increasing the number of troops along its border.
"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," Prime Minister Tayyip Erdogan's office said in a statement.
"Turkey will never leave unanswered such kinds of provocation by the Syrian regime against our national security."
Syria said it was investigating the source of the mortar bomb and urged restraint. Information Minister Omran Zoabi conveyed his condolences to the Turkish people, saying his country respected the sovereignty of neighbouring countries.
Turkey's parliament was due to vote on Thursday on extending a five-year-old authorization for its military to carry out cross-border operations, an agreement originally intended to allow strikes on Kurdish militant bases in northern Iraq.
That vote would now be extended to include operations in Syria, a ruling party deputy told Turkish television.
Residents of Akcakale gathered outside the local mayor's office, afraid to return to their homes as the dull thud of distant artillery fire rumbled across the town.
"We haven't been able to sleep in our own homes for 15 days, we had to sleep in our relatives' houses further away from the border because it's not safe down there," said shopkeeper Hadi Celik, 42, a father of five who was among the crowd outside the mayor's office.
Washington sees Turkey as a pivotal player in backing Syria's opposition and planning for the post-Assad era. The White House said on Wednesday it stood by "our Turkish ally". But Ankara has found itself increasingly isolated and frustrated by a lack of international consensus on how to end the conflict.