Syrian forces battled rebels near the airport in war-battered Aleppo, Syria's state media said Friday, in the first official acknowledgment that fighting has reached the doorstep of the strategic site in the country's largest city.

In Damascus, activists reported heavy shelling and clashes in many areas, including western districts believed to have rebel pockets. Damascus-based activist Moaz al-Shami described the shelling as "nonstop" and said gunners were firing from the Qasioun mountains overlooking the city.

The fighting in Syria's two main cities showed the intensity of the civil war and the regime's inability to suppress the rebels despite their overwhelming firepower.

Rebel footholds in Aleppo have been the target of weeks of Syrian shelling and air attacks as part of wider offensives by President Bashar Assad's regime. Rebels have been driven from some areas, but the report of clashes near the airport suggests the battles could be shifting to new fronts.

Syria's official SANA news agency said "armed terrorist groups" -- the regime's phrase for rebels -- had been pushed out from areas on both sides of the airport, which is located about 15 kilometers (nine miles) southeast of Aleppo's historical center. The report did not make it clear whether the fighting was closer to the international airport or the adjacent military airfield, a base for carrying out airstrikes on rebel sites in the north.

Aleppo carries major symbolic and strategic value. It's the hub of northern Syria and close to rebel-held territory and critical supply corridors to the Turkish border.

Rebels have sought control of the ancient center, dominated by a medieval Crusader castle. That would deal an embarrassing blow to the regime's claim that its overwhelming firepower can halt opposition advances.

"Those who think that the Syrian Arab army will be defeated are dreaming," said Syria's Foreign Minister Walid Moallem in a state TV interview late Thursday.

Civilians, meanwhile, have been increasingly caught in the crossfire, and many are fleeing to safety in nearby Turkey.

The U.N. refugee agency spokesman Adrian Edwards said 3,500 people crossed into Turkey on Tuesday and Wednesday. Edwards told reporters in Geneva there are now almost 65,000 Syrians in nine refugee camps in Turkey, about 40 percent of them new arrivals this month. In Jordan, nearly 2,700 Syrians have entered since Tuesday, swelling the numbers there to more than 150,000.

Beyond the refugees who have fled to neighboring countries, the U.N.'s humanitarian chief Valerie Amos estimated that as many as 2.5 million people inside Syria need relief assistance.

At the same time, U.N. officials in Syria were starting to close down their military observer mission after failed international attempts to broker a cease-fire. The U.N. plans to keep a small liaison office to support any future peace efforts to end the more than 17-month conflict, which has turned into a civil war and which activists say has left more than 20,000 people dead and forced hundreds of thousands from their homes.

The U.N.'s assistant secretary-general for peacekeeping, Edmond Mulet, said both sides have "chosen the path of war."

The core of Assad's military and political power appears to remain in place, but major cracks have emerged in the wider reaches of his regime. They include high-level military and political defections and the ability of rebel guerrillas to stage bombings and abductions in the heart of the capital, Damascus.

French Foreign Minister Laurent Fabius, who visited Syria's neighbors Jordan and Lebanon this week, told France's Europe-1 radio Friday that he was told "there will be new defections on a large scale." He gave no other details.

Fabius also defended France's refusal to send weapons to the Syrian rebels, despite their appeals for military help. He claimed rebel backers Qatar, Saudi Arabia and others are sending arms to the rebels -- although there has been no evidence of sharply enhanced military firepower by the anti-Assad forces.

"We Europeans decided on an arms embargo," he said. "We are not going to contradict our own positions."

In Lebanon, tensions from Syria have spilled over into the volatile patchwork of factions backing the rebels and others firmly behind Assad's regime, such as Iranian-backed Hezbollah.

A powerful Shiite Muslim clan in Lebanon claims to hold more than 20 Syrian nationals and a Turk in retaliation for the seizure of a family member by rebels in Syria this week. The clan said Thursday it was calling off "military operations" and would halt abductions for now.

Another captive was taken by unknown gunmen. Turkey's Foreign Ministry said a Turkish truck driver, Abdel Basit Erslan, was seized as he was driving in the Beirut suburb of Choueifat. It was unclear who was behind the abduction Thursday night.