Technical experts said the Internet shutdown was highly likely to have been caused by authorities throwing the "kill switch" on communications.
But this was met with denials from government officials, who on Thursday blamed the blackout on a “terrorist” attack or a technical fault.
President Bashar al-Assad's government has been accused before of cutting Internet and telephone connections to block opposition activists and rebel communications during the 20-month revolt.
According to AFP news agency, the Internet was back in Damascus and in parts of Damascus province.
Syrian opposition fighters battled regime troops south of Damascus Friday and Internet and most telephone lines were cut for a second day, but the government reopened the road to the capital's airport in a sign that the fighting could be calming, activists told the Associated Press.
Activists say Assad's regime pulled the plug on the Internet on Thursday, perhaps in preparation for a major offensive. Cellphone service also went out in Damascus and parts of central Syria, they said. The government blamed rebel fighters for the outages.
Thursday's violence appeared to be focused on southern suburbs near the airport, forcing the military to shut the road to the facility. The surrounding districts have been strongholds of rebel support since the uprising began.
On Friday, global hacking network Anonymous said it will shut down Syrian government websites around the world in response to the countrywide Internet blackout believed to be aimed at silencing the opposition to Assad.
Army shells Damascus outskirts
Meanwhile, the Syrian army shelled the outskirts of Damascus on Saturday in a drive to establish a secure perimeter around the capital.
The army targeted several villages near the key Damascus airport road that has come under sustained rebel attack, a monitoring group said.
The 27-kilometre (17-mile) highway remained perilous a day after troops said they had reopened the link to the outside world in heavy fighting that followed deadly fire on a bus carrying airport staff and at least two attacks on U.N. convoys, said the Syrian Observatory for Human Rights.
Troops were in action against rebels 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 Observatory, which relies on a network of activists and medics on the ground.
A Daraya-based activist told AFP 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.
At least 120 people were killed across Syria by security force gunfire on Saturday, according to activists at the Local Coordination Committees.