Turkey says its military has attacked targets inside neighboring Syria after mortar fire from Syria struck inside Turkey and killed five Turkish civilians and wounded about a dozen more.
A statement from Prime Minister Recep Tayyip Erdogan's office said Turkish forces had targeted "places in Syria identified by radar."
Earlier on October 3, a mother and four children were reported killed in the Turkish village of Akcakale by a mortar round fired from Syria.
The statement said, "Turkey will never leave unanswered such kinds of provocation by the Syrian regime against our national security."
Turkey's NTV television said Turkish radar pinpointed the positions from where the shells were fired on Akcakale, and that those positions were hit.
The statement said Foreign Minister Ahmet Davutoglu had spoken by telephone with UN Secretary-General Ban Ki-moon and the foreign ministers of several UN Security Council members about the incident.
Ban later urged the Syrian government to respect the territorial integrity of its neighbors and warned that the 19-month-long conflict in Syria is increasingly harming other countries in the region.
At a late-night meeting in Brussels, NATO ambassadors called on Syria to immediately end its "aggressive acts" against NATO member Turkey, pledging its full support to Ankara.
In Washington, U.S. Secretary of State Hillary Clinton said she was "outraged” over the shelling of Turkey from Syria.
"We are very regretful about the loss of life that has occurred on the Turkish side," Clinton added.
Pentagon press secretary George Little said the United States would closely monitor the situation closely.
Turkish media, meanwhile, reported Turkey has prepared legislation for Syria that is similar to one that authorizes the Turkish military to cross into northern Iraq in pursuit of Kurdish militants who have bases there.
On October 2, Russia cautioned NATO and other powers not to seek a "pretext" to intervene militarily in Syria's bloody conflict.
In an interview with the Interfax news agency, Deputy Foreign Minister Gennady Gatilov also called for restraint between NATO-member Turkey and Syria.
Gatilov's comments came after Erdogan recently criticized Russia for blocking efforts at the UN to exert pressure on Syrian President Bashar al-Assad and said Moscow's stance allowed massacres to continue in Syria.
Turkey's government has taken a hard line against violence leaking over into Turkey from the 19-month-old Syrian conflict.
Earlier on October 3, at least 31 people were killed and 90 wounded after three large explosions in the center of Aleppo
, Syria's biggest city.
The government blamed the explosions near the Aleppo Palace Hotel on suicide bombers. The alleged target was a nearby military officers' club.
State television broadcast footage showing major damage to the hotel and nearby cafes, and a large crater in Al-Jabari Square.
Syria's Interior Ministry vowed to "track down the perpetrators anywhere."
The speaker of the Syrian parliament, Mohammad Jihad al-Lahham, condemned "the countries that conspire against Syria and stand behind the terrorists."
With reporting by Reuters, AP, and dpa