A Syrian fighter jet has bombed the town of Ras al-Ain near the border with Turkey, a Reuters witness has said.
Forces loyal to Syrian President Assad bombarded Ras al-Ain over the weekend.
The town fell to the Free Syrian Army on Thursday, sending 9,000 fleeing the area within a day.
Thousands more refugees pour across the border to escape the war in Syria, whilst Turkey says the conflict is threatening their security.
A suggestion that David Cameron has gone "out on a limb" over Syria has been rejected by his official spokesman.