Ankara - Turkish troops pounded targets in Syria on Thursday morning in reprisal for cross-border fire that killed five Turkish civilians the previous day, a security source said.
"Artillery fire resumed at 0300 GMT this morning," the source said on condition of anonymity.
Several Syrian soldiers have been killed as a result of overnight Turkish shelling across the border, the Syrian Observatory for Human Rights watchdog said earlier, without giving an exact figure.
Turkey has demanded that the UN Security Council take action against Damascus after Wednesday's attack, which saw mortar fire from Syria kill five Turkish nationals, including a mother and her three children.
It marked the first time that Turkish citizens have been killed as a result of fire from its war-torn neighbour and led to a sharp escalation of tensions between the former allies.
Later on Thursday the Turkish parliament was due to consider a government request to approve cross-border military action.
Before Wednesday, the most serious clash between Syria and Turkey was in June, when Syria shot down a Turkish fighter jet, killing both crewmen.