BEIRUT -- Syrian rebels have begun a major operation in the Aleppo region, aiming to strike at security compounds and bases around Syria's largest city, activists said Friday.
It would be evidence that weeks of intense bombardments by the Syrian military, including airstrikes, have failed to dislodge the rebels. Instead, fighting rages across the country in a 17-month civil war that shows no sign of ending soon.
The rebel offensives in Aleppo are led by a brigade made up mostly of army defectors who specialize in operating artillery and tanks, said Mohammed Saeed, an activist based in the city.
He said the first attacks began shortly before midnight Thursday and lasted until Friday, when the "Brigade of Free Syrians" launched coordinated strikes on several security compounds in Aleppo.
"The new operations aim to strike at regime forces' centers and air bases throughout Aleppo (province)," Saeed said via Skype.
The Britain-based Syrian Observatory for Human Rights said one of the targets was a compound in the Aleppo neighborhood of Zahraa, where rebels killed and wounded a number of troops. It gave no figures.
Saeed said rebels attacked four security buildings around Aleppo, using tanks, rocket launchers and machine guns.
The state-run news agency, SANA, said troops killed and wounded several gunmen in the clashes.
Rebels took parts of Aleppo, Syria's commercial capital, last month. Since then, government forces have been trying to recapture them. Rebels also control much of the wider Aleppo province, including areas on the border with Turkey.
Activists estimate more than 20,000 people have been killed in the uprising against President Bashar Assad's regime.
There has been fighting all over Syria, including the capital, Damascus, showing that the rebels have a presence in main population centers, not just the outlying districts where they started.
The Observatory and the Local Coordination Committees, another activist group, reported clashes and shelling between troops and rebels in other areas, including the southern province of Daraa, around Damascus and in the central region of Homs.
The Observatory reported heavy clashes inside the sprawling Abu Zuhour air base in the northwestern province of Idlib, saying that anti-government gunmen were advancing, storming officers' housing units. The clashes in and around Abu Zuhour air base have been going on for the past two days. The reports could not be confirmed independently.
Syrian rebels said they shot down a Russian-made MiG fighter jet over Idlib on Thursday.
Over the past month, the Syrian regime has been relying much more heavily on air power, escalating the fight with rebels as its ground forces have been stretched thin fighting on many fronts. The military has conducted air raids on the northern regions of Idlib and Aleppo near Turkey as well as the eastern province of Deir el-Zour.
The increased use of air power is likely a factor in the high daily death tolls, which activists say have been averaging 100 to 250 lately.
In Geneva, the U.N. refugee agency reported a growing number of Syrians fleeing to Lebanon's eastern Bekaa Valley, near the Syrian border.
Agency spokesman Adrian Edwards said local authorities report that about 2,200 people arrived there over the past week, almost double the weekly average. He told reporters Friday in Geneva that another 400 Syrians are reaching northern Lebanon each week.
Edwards said Turkey has opened two more refugee camps for Syrians in the past week and is now hosting 80,410 people in 11 camps and schools in its border provinces.
In France, Foreign Minister Laurent Fabius warned that France would use military force if President Bashar Assad ever uses his chemical weapons. "Our response would be immediate and sharp as lightning," Fabius said Friday on Europe-1 radio.
He suggested that France would not wait for U.N. permission for such a response. "Bacteriological and chemical weapons are of a different nature from ordinary arms," he said. "We cannot tolerate that these weapons, whose fallout could spread, would be used."
Last month, Syria threatened that if it has chemical and biological weapons, it would use them to face a foreign attack.