The Syrian army shelled the outskirts of Damascus on Saturday in a drive to establish a secure perimeter around the capital, including the key airport road that has come under sustained rebel attack.
The 27-kilometre (17-mile) highway remained perilous a day after troops said they had reopened the key link to the outside world in heavy fighting that followed deadly fire on a bus carrying airport staff and at least two attacks on UN convoys, a watchdog said.
Syrian Internet and mobile phone links remained cut for a third straight day, an AFP correspondent in Damascus reported, amid US accusations the government is deliberately seeking to deprive the opposition of communications.
Troops were in action against rebel fighters entrenched in both the southwestern outskirts of the capital and the eastern suburbs, where the airport lies, human rights monitors and opposition activists said.
Southwest of the capital, "the army shelled orchards that extend from Kfar Sousa to Daraya and are taking on rebels who control the region," said the Syrian Observatory for Human Rights, which relies on a network of activists and medics on the ground.
A Daraya-based activist told AFP by satellite link that regime forces were using warplanes and tanks to hit the town.
"We are hiding in shelters, but casualties from the shelling is very high," said the activist, who identified himself only as Abu Kinan.
Observatory director Rami Abdel Rahman told AFP there had been intermittent battles from early morning between Damascus and the international airport.
"The army used warplanes, helicopter gunships and tanks to shell several villages in that area, including Babila, Beit Sahn and Aqraba," he said. "The army's operation to secure that area has continued."
Analysts say President Bashar al-Assad's regime has been trying to establish a secure perimeter around Damascus at all costs in a bid to be in a position to negotiate a solution to the 20-month conflict that monitors say has cost more than 41,000 lives.
The repeated firing on the airport road prompted the cancellation of a string of international flights.
Airport officials said flights had resumed on Friday but a military source acknowledged several days' more fighting lay ahead to fully secure the road.
Signup to our newsletter and follow us on Facebook and Twitter!
Clashes between troops and rebels also rocked Syria's second city Aleppo, scene of urban warfare for more than four months, the Observatory said.
Fourteen rebels were killed in fighting near an air base southwest of the city, it added.
-- Syria army re-enters oilfield --
In the east, troops re-entered the Al-Omar oilfield, three days after pulling out, the Observatory said.
"Despite Thursday's pullout, rebels did not enter the oilfield for fear that it was mined," said Observatory director Rami Abdel Rahman.
The oilfield is one of the regime's last positions east of the city of Deir Ezzor. Last week, rebels seized a huge swathe of territory stretching from the city to the Iraqi border, the largest in Syria outside government control.
Early last month, the rebels seized control of the Al-Ward oilfield, the first it had captured. The army has since also lost control of the Al-Jofra oilfield and the Conoco gas reserves, according to the Observatory.
Syria's oil and gas production is now largely for domestic consumption as a result of embargos on its exports by its biggest pre-conflict customers. But rebel activity has also taken a mounting toll on output.
Violence nationwide killed at least 37 people on Saturday, among them 15 civilians, according to a preliminary toll from the Observatory.
The watchdog's chief said the continuing blackout of Internet and mobile phone connections was hitting ordinary civilians harder than opposition activists.
"Many activists have satellite phones, but the average Syrian who needs to make a mobile phone call to get help for an injured person, for instance, can no longer do so," Abdel Rahman said.
Google and Twitter said that they had reactivated a voice-tweet program to allow Syrians affected by an Internet shutdown to get messages out. It was last used in 2011, when the Internet was shut down in Egypt during its revolution, bur/kir/al