Fierce fighting has been reported on the road that links Damascus to the Syrian capital's airport, as internet and telecommunications links within the country remain largely blacked out.
Clashes were reported along the 27km-long road, with the government saying that it had now secured the route and that international flights were free to resume on Friday. Rebels disputed that claim.
"After strong clashes, rebels were able to take control of a part of the airport road between the second and fourth bridge," activists said.
State television had on Thursday night quoted the information ministry as saying that the airport road, closed for much of the day due to the fighting, had been "secured" after military intervention.
Both EgyptAir and Emirates had on Thursday announced suspension of flights due to the fighting.
A Syrian security source said: "[On Thursday], we sent a telegram to the foreign companies still working in Syria and SyrianAir [the national carrier] to inform them of the status of the road to the airport so they would cancel their flights to Damascus."
"Today after the road was secured, we sent a new telegram to inform them that security was restored," she told AFP.
A military source in Damascus said that the army had taken control of the western side of the road leading to the airport and a small portion on the east by dawn, allowing travellers to move through.
"But the most difficult part is yet to come. The army wants to take control of the eastern side, where there are thousands of terrorists and this will take several days," he said, using the term regime officials use to describe rebel fighters.
Meanwhile, at least 17 Lebanese fighters have gone missing after an ambush by government forces inside Syrian territory. The fighters were part of a group of 20, mostly from the Lebanese city of Tripoli, who were travelling to Syria with the intention of joining rebel forces in Homs.
Three of the fighters escaped the ambush and were able to return to Lebanon, Al Jazeera's Mysa Khalaf reported from Beirut.
As violence continued, the blackout of phone and internet networks remained in place across most of Syria for a second straight day.
The length of the internet blackout, which continued on Friday, is unprecedented in Syria's 20-month-old uprising against President Bashar al-Assad.
Renesys, a US-based company that monitors online connectivity, confirmed that "all 84 of Syria's IP address blocks had become unreachable [on Thursday], effectively removing the country from the Internet".
In-depth coverage of escalating violence across Syria
Residents in some areas reported on Friday that they could access the internet but "with great difficulty".
"It is also very difficult to reach people by phone," Rami Abdel Rahman, the head of the Syrian Observatory for Human Rights, reported.
"But we have received reports that it is possible to communicate between certain regions via fixed telephone lines."
AFP news agency correspondents noted that internet and telephone communications, including mobile phones, were cut in the capital.
The official news agency SANA had still not resumed transmission on Friday after its feed was cut on Thursday at midday. The agency's website was also inaccessible.
Google and Twitter announced on Friday that they had reactivated a voice-tweet programme to allow Syrians affected by the shutdown of the Internet to get messages out. The service allows people with a telephone connection to compose and send a tweet by speaking on their phones.
Syrian state TV denied the blackout was nationwide. It said the outage was caused by a technical failure, only affected some provinces, and that technicians were trying to fix the problem.
Syria's minister of information said "terrorists", not the state, were responsible for the outage, a pro-government TV station reported. Internet companies said that this was unlikely.
The US on Thursday accused the Syrian government of cutting off internet and telecommunications links in the war-torn country, branding the move a sign of desperation.
Amnesty International said on Twitter that reports of an internet shutdown were "very disturbing".
The government has previously cut phone lines and internet access in areas where its forces are about to conduct major military operations.