Battles between Syrian rebels and government troops have reportedly forced the closure of the main road leading to Damascus International Airport.
The news came as the Dubai-based Emirates airline suspended flights to the Syrian capital on Thursday.
The UK-based Syrian Observatory for Human Rights (SOHR) said there was heavy fighting "along all the areas along the road" to the airport, southeast of the city.
The activist group said clashes were particularly intense in Babbila, a suburb bordering the rebel stronghold of Tadamoun.
State media later reported that the road had been "secured" after military intervention in the area.
"The road from the airport was secured after attacks by armed terrorist groups against cars and after a deployment of the competent forces," state television quoted the the information ministry as saying.
Meanwhile, residents and internet-monitoring companies said internet was cut off nationwide.
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Renesys, a US-based network security firm that studies internet disruptions, said Syria effectively disappeared from the internet at 12:26pm local time.
In parts of Damascus, mobile and land telephone lines were only working intermittently.
The government has previously cut phone lines and internet access in areas where regime forces are conducting major military operations but a nationwide internet shutdown is unprecedented.
Syria's minister of information said "terrorists", not the state, were responsible for the internet outage, a pro-government TV station reported.
"It is not true that the state cut the internet. The terrorists targeted the internet lines, resulting in some regions being cut off," he was quoted by al-Ikhbariya as saying.
State TV quoted the telecommunications minister as saying engineers were working to repair what he said was a fault in the main communications and internet cable.
Emirates said it was suspending daily flights to Damascus "until further notice", but other airlines continued operations.
Airport sources in Cairo said an Egypt Air flight that left at 1:30pm (11:30 GMT) had landed in Damascus as scheduled.
"The Egypt Air plane has arrived ... and passengers are all safe but the pilot was instructed to take off back to Cairo without passengers if he felt that the situation there is not good to stay for longer," an official at Cairo airport said.
Elsewhere in the capital, warplanes bombed the neighbourhoods of Kafr Souseh and Daraya, opposition activists said.
Rebels who control large swathes of territory in northern Syria have made military gains in past days, including for the first time shooting down one of the regime's attack aircraft using a surface-to-air missile.
Several rebel brigades attacked the Wadi Daif base in Idlib province on Thursday, opposition sources said, while the army responded with shelling.
Fighting was also reported outside the nearby rebel-held town of Maaret al-Numan.
In the country's commercial capital, Aleppo, an air strike on Thursday killed at least 15 civilians, according to the SOHR.
"At least 15 people, among them five children and two women, were killed when a warplane dropped two bombs on the Ansari district of Aleppo," the group's head Rami Abdelrahman told the AFP news agency.