"The battles were flaming throughout the day," he said, asking not to be identified because he was afraid of repercussions.
But much of Thursday's violence was focused on southern suburbs near the airport. The surrounding districts have been strongholds of rebel support since the uprising began.
Two Austrian soldiers assigned to the United Nations Disengagement Observer Force in the Golan Heights were wounded Thursday when their convoy came under fire on the way to the airport, Austria Press Agency said.
The two were transferred to Israel for treatment Friday and their condition is not life-threatening, said David Ratner, a spokesman for Rambam Hospital in Haifa. He said the two soldiers suffered gunshot wounds — one to the chest and the other to the hand.
With pressure building against President Bashar Assad's regime on several fronts and government forces on their heels in the battle for the northern commercial hub of Aleppo, rebels have recently begun pushing back into Damascus after largely being driven out of the capital following a July offensive. One Damascus resident reported seeing rebel forces near a suburb of the city previously deemed to be safe from fighting.
Regime forces have suffered a string of tactical defeats in recent weeks, losing air bases and other strategic facilities. The government may be trying to blunt additional rebel offensives by hampering communications.
Analysts say the regime appears to be the culprit for the Internet outage. Syria has several cables that connect it to the outside world, and all of them would have had to be cut at once for a complete outage.
As the rebels and government vie for the upper hand in an increasingly bloody struggle, the conflict's toll on civilians is worsening.
The U.N. refugee agency said Friday it found desperate conditions in the Syrian city of Homs, where thousands of people are living in unheated shelters and a quarter of a million people are displaced from their homes.
An assessment team visiting this week saw half of the city's hospitals shut down and "severe shortages of basic supplies ranging from medicine to blankets, winter clothes and children's shoes," agency spokeswoman Melissa Fleming said.
As the violence rages, Syria's neighbors are increasingly being drawn into the country's civil war in a variety of ways, whether militarily or as a result of an exodus of Syrians fleeing the fighting.
Syria is believed to have several hundred ballistic surface-to-surface missiles capable of carrying chemical warheads — a particular concern for Turkey, a NATO member.
On Friday, NATO said it will deploy Patriot missiles to Turkey's border with Syria "within several weeks" after the move is approved.
Spokeswoman Oana Lungescu said a team assessing possible sites for the air defense systems is making good progress and is expected to report back soon. This opens the possibility that foreign ministers of the 28 member countries, meeting in Brussels on Tuesday and Wednesday, could make the final decision.
Germany, the Netherlands and the U.S. have the advanced PAC-3 model Patriots that Turkey needs to intercept ballistic missiles. Parliaments in Germany and the Netherlands must also approve the deployment.
Associated Press writer Albert Aji in Damascus, Syria, contributed to this report.