The Turkish provincial government said the shell may have targeted Syrian opposition forces on the border. It hit just outside a village about 500 feet inside Turkey, CNN reported.
Fighting between the two countries began Wednesday when a Turkish border town was shelled from Syria. Five civilians were killed and nine others injured.
Syria's ambassador to the United Nations Thursday expressed "deepest condolences" for the shelling and urged Turkey to show restraint.
Turkish Prime Minister Recep Tayyip Erdogan condemned the shelling Friday, but warned Syria "it would be a deadly mistake to test Turkey's deterrence, determination and capacity."
Opposition activists said fighting within Syria Saturday killed 37 people, including 23 in Homs.