New York Times News Service

BEIRUT — Rebel fighters and security forces in Syria clashed near the border with Lebanon and fought over a military barracks in Aleppo on Sunday, while Turkish artillery fired into Syria for a fifth consecutive day in retaliation for cross-border shelling.

On Sunday morning, Syrian forces shelled Tal Abyad, a Syrian border town where rebels recently seized control, according to anti-government activists. Video images posted online purported to show women and children fleeing the area.

Around the same time, a Syrian shell landed about 200 yards across the border from Tal Abyad, near Akcakale in Turkey, The Associated Press reported. Akcakale is where a Syrian mortar shell killed Turkish civilians Wednesday, prompting the Turkish government to announce a policy of retaliation for every shell that strays across the border. Turkish forces fired eight shells into Syria on Sunday. The mounting tensions at the border have raised international concerns that the 18-month-old internal conflict in Syria could draw in neighbors or even the NATO alliance, to which Turkey belongs.

In Aleppo, the government news service said, the army had killed “many terrorists” who tried to infiltrate a military barracks. Earlier, the anti-government Tawhid Brigade said its fighters had penetrated the Hanano military barracks Sunday and were fighting government forces inside the compound.