* Clashes along airport road heaviest during uprising
* Report of rebel mortars fired at airport runways
* Internet "shut down completely" - tracking service
* Rebels advancing but "not last days yet" for Assad
By Oliver Holmes
BEIRUT, Nov 29 (Reuters) - Syrian rebels battled forces loyal to President Bashar al-Assad just outside Damascus on Thursday, cutting access to its international airport, and Dubai-based Emirates airline and EgyptAir stopped flights to the Syrian capital.
The Internet and some telephone lines went down across Syria. Rebels and the government traded blame for the blackout, the worst communications outage in 20 months of conflict.
Rebels fighting to topple Assad have been making gains around Syria by overrunning military bases and have been ramping up attacks on Damascus, his seat of power.
A rebel fighter who identified himself as Abu Omar, a member of the Jund Allah brigade, told Reuters that insurgents fired mortars at the airport's runways and were blocking the road linking it with the capital.
Speaking from the scene of the fighting, he said insurgents were not inside the airport but were able to block access to and from it.
A spokesman for a rebel Military Council in Damascus, Musaab Abu Qitada, said an artillery round was fired at a military site inside the airport and that fighting was now less than a kilometre (mile) away from the complex.
"We want to liberate the airport because of reports we see and our own information we have that shows civilian airplanes are being flown in here with weapons for the regime. It is our right to stop this," he told Reuters on Skype from Damascus.
U.S. and European officials said rebels were making gains in Syria, gradually eroding Assad's power, but said the fighting had not yet shifted decisively in their favour.
Two Austrian soldiers in a U.N. peacekeeping force deployed to monitor the frontier with the Israeli-occupied Golan Heights were wounded when their convoy came under fire near Damascus airport, Austria's defence ministry said. Syria state television said the soldiers were wounded by gunfire when rebels attacked an army position near the airport road.
The Information Ministry later said the highway to the airport was safe after security forces cleared it of "terrorists." Rebels said fighting in the area was continuing. The ministry said the airport was operating regularly, but there were no flights scheduled to land in the evening.
The accounts of fighting could not be verified immediately because of tight restrictions on media access to Syria.
But many airlines had already halted flights. Emirates suspended daily service to Damascus "until further notice." EgyptAir also said it was suspending all flights to Damascus because of "the deterioration of the security situation" there.
An EgyptAir flight that left at 1:30 p.m. (1130 GMT) landed in Damascus on schedule but the pilot was instructed to take off straight back to Egypt, airport sources in Cairo said.
INTERNET, PHONE LINES DOWN
Residents said the Internet in Damascus crashed in the early afternoon, and mobile and land telephone lines were functioning only intermittently.
A blog post on Renesys, a U.S. company which tracks Internet traffic worldwide, said that at 12:26 pm (1026 GMT), the entire country's Internet connectivity shut down completely.
The government has been accused of cutting communications in previous assaults on rebel-held areas in Syria. Syria's minister of information said "terrorists" were responsible for the Internet shutdown, while the telecommunications minister blamed what he said was a fault in the main communications network.
The past two weeks have seen rebels seizing a series of army bases across Syria, exposing Assad's loss of control in northern and eastern regions despite the devastating air power that he has used to bombard opposition strongholds, killing dozens of civilians as well. More than 40,000 people have been killed since the uprising began, according to opposition groups.
Rebels and activists said the fighting along the road to Damascus airport, southeast of the capital, was heavier in that area than at any other time in the conflict.
"PREPARING FOR MAJOR BATTLE"
Nabeel al-Ameer, from the rebel Military Council, said a large number of army reinforcements had arrived along the road after three days of scattered clashes ending with rebels seizing side streets to the north of it.
He said he hoped the proximity of the rebels to the airport would dissuade authorities from using it to import military equipment, but the priority now was to block the road.
There are several military airports around Damascus that remain under government control.
A Syrian security source told Reuters on condition of anonymity that the army had started a "cleansing operation" in the capital to confront rebel advances.
The source, who is from Assad's elite 4th Armoured Division, said one of the aims of the operation was to seal off the suburbs - where rebels are dominant - from the city center.
Assad is fighting an insurgency that grew out of peaceful demonstrations for democratic reform but has escalated, after a military crackdown on protesters, into a bloody civil war.
Syrian warplanes on Thursday bombed Kafr Souseh, Douma and Daraya, neighbourhoods that fringe the center of the city where rebels have managed to hide out and ambush army units.
Activists said the areas were taking one of the heaviest poundings they had seen in months.
A senior European Union official said that Assad - whose family has held power in Syria for 42 years - might be preparing for a military showdown around Damascus by isolating the city with a network of checkpoints.
"The rebels are gaining ground but it is still rather slow. We are not witnessing the last days yet," the official said on condition of anonymity.
"On the outskirts of Damascus, there are mortars and more attacks. The regime is thinking of protecting itself ... with checkpoints in the next few days ... (It) seems the regime is preparing for major battle on Damascus."
A U.S. official said the rebels were "making important tactical gains that could eventually trigger a strategic shift in the conflict."
"They haven't reached that point yet, but the span of regime control is narrowing, and Assad's forces are having greater difficulty beating back the insurgents' progress," said the official, who also spoke on condition of anonymity.
Secretary of State Hillary Clinton echoed that view in remarks in a speech in Washington.
"I don't know that you can say that for the entire country it is yet at a tipping point, but it certainly seems that the regime will be much harder pressed in the next months," she said.
WARY BIG POWERS
Most foreign powers have condemned Assad but stopped short of arming rebel fighters as they fear heavy weapons could make their way into the hands of radical Islamist units, who have grown increasingly prominent in the insurgency.
Rebels decry their supporters for not providing them with surface-to-air missiles that they say they need to counter the air force. But recent looting of anti-aircraft missiles from army bases, as well as a slow stream of such weapons believed to be coming from Gulf Arab adversaries of Assad, has allowed them to shoot down some helicopters and jets.
U.S. Defense Secretary Leon Panetta told a Pentagon news conference the United States had not provided anti-aircraft missiles to the Syrian opposition, saying it was focused on nonlethal aid and humanitarian relief.
"Let me say unequivocally that we have not provided any of those kinds of missiles to the opposition forces located in Syria," he said.
Panetta and Israeli Defense Minister Ehud Barak both told the news conference they believed Assad would ultimately fall.
"It's criminal behavior on a global scale what he is doing to his own people, using jet fighters and helicopters and artillery and tanks, killing his own people," Barak said. "The whole world is watching and somehow it's not easy to mobilize enough sense of purpose and unity of action and political will to translate ... our feelings about what happens there into action to stop it."
Peter Bouckeart, emergencies director at Human Rights Watch, said the surface-to-air missiles used so far appeared to have been captured from the Syrian military and there was no evidence any of the ones used to date "have come from outside Syria."
He said the number of these missiles in rebel hands was probably over 20 but could rise significantly if rebels continue to capture military bases.
The relatively small number of anti-aircraft missiles looted so far means that many rebel-controlled areas of the country remain vulnerable to air strikes. The Observatory said 15 citizens, including children and women, were killed during a bombing in Aleppo's Ansari district on Thursday.