At Turkey’s request, NATO representatives held an emergency session to discuss the incident. Erdogan said Foreign Minister Davitoglu also contacted the members of the U.N. Security Council and NATO Secretary-General Anders Fogh Rasmussen. Davitoglu said he also had contacted U.N. Secretary-General Ban Ki-moon and special U.N. Syria negotiator Lakhdar Brahimi.

Ban urged Syria to respect the territorial integrity of its neighbors and to stop shooting at its own people.

“The secretary-general has repeatedly warned that the ongoing militarization of the conflict in Syria is leading to tragic results for the Syrian people," he said in a statement.

“Today’s incidents, where firing from Syria struck a Turkish town, again demonstrated how Syria’s conflict is threatening not only the security of the Syrian people but increasingly causing harm to its neighbors," it said.

Turkey has openly sided with the rebels, who Syria says routinely take shelter inside Turkey. But Turkey denies accusations that it has given any direct military help to the armed groups.

An estimated 90,000 Syrians have taken refuge inside Turkey as fighting has raged. The number of Syrian refugees has surged since rebels launched an offensive in July to seize Aleppo, Syria’s largest city, which lies about 50 miles from Akcakale.

Syrian artillery fire, sometimes from a distance, has crossed the border before. In the area around the Syrian-Turkish border crossing near the Syrian city of Kasab, the woods on both sides of the mountainous border are burned from Syrian shelling.

Meanwhile, SANA, Syria’s state news agency, reported that at least 34 people were killed and 122 injured in a series of suicide car bombings in Aleppo on Wednesday that the government blamed on rebel forces.

The news agency said two car bombs were detonated in the city’s Saadallah al-Jabri Square shortly before 8 a.m., stripping buildings of their facades and leaving deep craters in the streets. Another car, this one loaded with 1,100 pounds of explosives, exploded 25 minutes later outside the provincial capital building. At the same time, two mortar rounds fell near Aleppo’s city hall, SANA reported.

The final blast came at 10:35 a.m., the news agency reported, as security officers were attempting to disarm a car bomb carrying more than a ton of explosives. The explosion, which SANA said had been triggered by remote control, ripped through the Aleppo Chamber of Commerce and the Central Bank.

Special correspondent David Enders contributed from Beirut. Jonathan S. Landay contributed from Washington