Syrian troops mounted an assault on rebels near Damascus on Thursday, closing off the road to the airport before later securing it, authorities said, amid a widespread telecommunications outage.
Meanwhile, as UN envoy Lakhdar Brahimi hinted President Bashar al-Assad would have to step down to allow for a new Syria, a monitoring group said a government air raid on the northern city of Aleppo killed at least 15 civilians.
The Syrian Observatory for Human Rights said the army attacked rebel bastions in a string of towns along the highway and near the international airport, with state media saying the road was eventually "secured."
The fighting around the capital, which came after Internet links went down across Syria, prompted EgyptAir and Emirates to announce the cancellation of flights to Damascus.
Official media said several members of an "armed terrorist group, Al-Nusra Front," had been killed in the town of Aqraba.
Two Austrian soldiers with a UN force on the Golan were injured after their convoy was shot at on the road to the airport, the foreign ministry in Vienna said.
A ministry spokesman said one soldier was shot in the arm, and the other in the shoulder, but both were quickly treated.
Austrian Foreign Minister Michael Spindelegger instructed his country's embassy in Damascus to file a protest with the government and the Syrian ambassador in Vienna was to be summoned to the foreign ministry.
"Syria is responsible for the safety of our UNDOF soldiers and must ensure that they can fulfil their international mandate," Spindelegger said.
In Syria, state state television, quoting a foreign ministry source, blamed the shootings on rebels.
"At around 12 noon (1000 GMT), and while a terrorist armed group was firing towards an army post in the area of Aqraba, the shots hit a vehicule of UNDOF, leading to the injury of two members of those forces," it said.
As activists warned that sudden communication cuts are often a signal of imminent military offensives, US technology companies Akamai and Renesys, which monitor web traffic, said the country was cut off from the Internet.
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In Damascus, users said both Internet and mobile telephone communications were cut and land lines barely functioning, with the country's Internet provider citing technical problems.
The United States accused the beleaguered Syrian regime of deliberately severing telecommunications links in what it branded a sign of desperation.
"We condemn this latest assault on the Syrian people's ability to express themselves and communicate with each other and it just, again, speaks to the kind of desperation of the regime," State Department spokeswoman Victoria Nuland said.
She added, however, that some 2,000 communications sets supplied to opposition rebels over recent months as part of a US non-lethal assistance programme were not affected by the blackout.
Amnesty International warned that the cut in telecommunications "may herald the intention of the Syrian authorities to shield the truth of what is happening in the country from the outside world."
In northern Syria, five children and two women were among at least 15 people killed when a government warplane dropped two bombs on the rebel-held Ansari district of Aleppo, the Britain-based Observatory said.
The strike hit two buildings in Aleppo, the commercial capital, and videos posted online by activists showed the facades of several apartments blown away.
Rebels, who control vast swathes of territory in northern Syria, have made significant gains in past days, including shooting down regime attack aircraft with surface-to-air missiles for the first time.
The Washington Post reported on Thursday that Syrian rebels have obtained up to 40 shoulder-fired anti-aircraft missiles, some from Qatar, citing Western and Middle Eastern intelligence officials.
Analysts say the delivery marked a potential turning point in the prolonged war with Assad's forces, in which the Observatory says more than 40,000 people have perished since March 2011.
On Thursday, it said at least 59 people died nationwide -- 34 civilians, 19 soldiers and six rebels.
On the diplomatic front, international envoy Brahimi briefed the UN Security Council, which remains divided between Western nations and Assad allies Russia and China on the 20-month conflict.
"I think it's very, very, very clear that the people of Syria want change, and real change, not cosmetic changes," he later told reporters in New York. "The new Syria will not look like the Syria of today."
Brahimi also said that Syria "very, very urgently" needed a ceasefire and a large peacekeeping force. "A ceasefire will not hold unless it is very, very strongly observed. That, I believe, will require a peacekeeping mission."