CEYLANPINAR, Turkey A Syrian warplane struck homes in the town of Ras al-Ain on Tuesday within sight of the Turkish border, pursuing an aerial bombardment to force out rebels and drawing a new warning from Ankara.
The second day of jet strikes sent Syrians scurrying through the flimsy barbed-wire fence that divides Ras al-Ain from the Turkish settlement of Ceylanpinar as thick plumes of smoke rose above the town.
Medical workers and refugees in Ceylanpinar said bombing on Monday and Tuesday struck residential areas of Ras al-Ain, which fell to rebels last week during an advance into Syria's mixed Arab and Kurdish northeast.
The offensive has caused some of the biggest refugee movements since the armed revolt against President Bashar al-Assad began in March last year, and brought the war back perilously close to Turkish soil.
Turkey is reluctant to be drawn into a regional conflict but the proximity of the bombing raids to the border is testing its pledge to defend itself from any violation of its territory or any spillover of violence from Syria.
Turkish Prime Minister Tayyip Erdogan stressed that Ankara would not hesitate to respond if threatened.
"We are giving the necessary response on the border and will not refrain from a much harsher response if necessary," he told deputies of his AK Party. "Nobody should play with fire or try to test Turkey's patience."
A Turkish health official at the hospital in Ceylanpinar said rebel fighters were trying to pull the wounded from under the rubble of a house. Refugees say the fighters are taking cover in homes, many of them abandoned by residents who have fled for Turkey.
"As soon as we heard the jets, we knew they would bomb. It hit another house just 100 metres away," Mohammad Kahan, 49, a Kurd who fled Ras al-Ain with nine members of his family, said of Monday's bombardment.
"This won't stop, Assad will not go until America and Britain come and stop him. Only these two can stop him."
Opposition activists say at least a dozen people died on Monday, the latest of an estimated 38,000 victims of the 19-month civil war. The casualty toll on Tuesday was not known.
Turkey has repeatedly fired back in retaliation for stray gunfire and mortar rounds flying across its 900 km (560 mile) border with Syria, and is talking to NATO allies about the possible deployment of Patriot surface-to-air missiles.
Ankara says this would be a defensive step, but it could also be a prelude to enforcing a no-fly zone in Syria to limit the reach of Assad's air power. Western powers have so far been reluctant to take such a step.
Rebels fired machineguns mounted on pick-up trucks at the jet as it swooped low over Ras al-Ain, dropping three bombs before returning for a second strike on another part of the town, said a Reuters witness on the Turkish side of the border.
Ambulances with sirens wailing ferried the wounded from the border for treatment in Ceylanpinar.
In one 24-hour period last week, some 9,000 Syrians fled fighting during a rebel advance into Syria's northeast, swelling to over 120,000 the number of registered refugees in Turkish camps, with winter setting in.
Tens of thousands more are unregistered and living in Turkish homes.
(Additional reporting by Ece Toksabay; Writing by Matt Robinson; Editing by Tom Pfeiffer)