Another 11,000 escaped to Turkey last week following the surge of fighting at Ras al-Ayn, which is located in the northeastern Syrian province of al-Hasaka, an oil-producing region where the population is mostly Kurdish.

The proximity of the fighting to Turkey has raised fears of an escalation.

Turkish media, including the Anadolu news agency, said several villages west of Ceylanpinar have been evacuated to protect residents from any spillover of the fighting in Syria. About 1,000 people left Mursitpinar, 110 miles (180 kilometers) from Ceylanpinar, after an appeal from the loudspeakers of local mosques.

Ismet Yilmaz, Turkey’s defense minister, indicated that military force would be used in response to any incursions by Syrian aircraft. Last month, Turkish artillery fired on targets in Syria after Syrian shells landed inside Turkey and killed several civilians.

‘‘The necessary response will be given to Syrian planes and helicopters that violate our border,’’ Yilmaz said.

A Turkish official in Ceylanpinar said the sound of shelling was heard through the night. Two rocket-propelled grenades hit houses on the Turkish side, but there were no injuries, according to the official, who spoke on condition of anonymity because he is barred by rules from being quoted by name.

The official later said a dozen wounded Syrians had been brought across the border, and one died during treatment. The official cited contacts in Ras al-Ayn as saying Syrian forces had entered the town.

A convoy of seven white jeeps and a truck was seen near the Syrian town, but it was unclear who was in the vehicles. On the Turkish side of the border, Turkish jets were heard overhead.

At one point, sounds of jubilation were heard from Ras al-Ayn. One rebel shouted in Arabic: ‘‘The Syrian army fled. Did you see?’’

The Syrian Observatory for Human Rights said warplanes carried out six airstrikes in al-Hasaka, including those at Ras al-Ayn.

Regime fighter jets also targeted the rebellious suburbs of Damascus on Wednesday, the Britain-based Observatory said. Heavy clashes between rebel units and Assad’s troops were ongoing in the northern city of Aleppo, the Observatory said. The group relies on reports from activists on the ground.

Although the conflict has been grinding on for nearly 20 months, neither side has managed to strike a blow that could tip the balance.

Over the weekend, Syria’s splintered rebel factions agreed to a U.S.-backed plan to unite under a new umbrella group that seeks a common voice and strategy against Assad’s regime.

President Barack Obama said he’s encouraged the opposition has formed a new, more representative leadership council, but the U.S. isn’t ready to recognize the group as a ‘‘government in exile’’ or to arm it.

‘‘We consider them a legitimate representative of the aspirations of the Syrian people,’’ Obama said at a news conference at the White House.

France was the first Western country to formally recognize the newly formed opposition coalition as the sole legitimate representative of the Syrian people.

Obama said the U.S. wanted to make sure the group ‘‘is committed to a democratic Syria, an inclusive Syria, a moderate Syria.’’ He also said the U.S. isn’t considering sending weapons to the opposition because of concerns the arms might fall into the hands of extremists.

‘‘We have seen extremist elements insinuate themselves into the opposition and one of the things that we have to be on guard about, particularly when we start talking about arming opposition figures, is that we are not indirectly putting arms in the hands of folks that would do Americans harms, or do Israeli harm or otherwise engage in actions that are detrimental to our national security,’’ he said.

The outgunned rebel fighters want arms — including critical anti-aircraft batteries — from main regional backers such as the wealthy Gulf states and Turkey.

Syrian Information Minister Omran al-Zoebi brushed off the new opposition group as a ‘‘desperate attempt’’ to undermine Syrians’ morale.

Foreign ministers from the main Gulf Arab bloc — which includes key rebel backers Saudi Arabia and Qatar — met Wednesday in the Saudi capital Riyadh to discuss the crisis, according to the official Saudi News Agency. The talks were expected to bring in visiting Russian Foreign Minister Sergey Lavrov, whose nation is an important ally of Syria.

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