Syrian troops mounted an assault on rebels near Damascus on Thursday, closing off the road to the airport amid a widespread telecommunications outage, as the US weighed what further help it can give the rebels.
Meanwhile, as UN envoy Lakhdar Brahimi hinted that 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 "armed terrorist group, Al-Nusra Front", had been killed in the town of Aqaba.
Two Austrian soldiers with the UN force on the Golan Heights were shot and wounded in Syria while their convoy was travelling to Damascus airport, the defence ministry in Vienna said.
The pair, whose lives were not in danger, were travelling to Damascus airport to fly back to Austria after their tour of duty, the ministry said.
Two more soldiers in the Austrian convoy were lightly injured by fragments, it added.
It was unclear whether they were shot by Syrian government forces or rebels, according to a ministry spokesman.
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.
In Damascus, users said both Internet and mobile telephone communications were cut and landlines were 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 said was 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.
Washington was meanwhile weighing what further help it can give the rebels, Secretary of State Hillary Clinton said Thursday, without spelling out if they would win full US recognition.
"We are going to carefully consider what more we can do," Clinton told a Washington forum, saying the United States was constantly evaluating the situation and adding: "I'm sure we will do more in the weeks ahead."
"If this were a straightforward challenge I think we would all have reached a conclusion and have unified behind exactly what we are going to do, and how to do it," she told a conference organized by Foreign Policy magazine.
But she stopped short of saying whether the United States would recognize the newly-formed Syrian National Coalition, which is seeking to oust Assad, as the sole representative of the Syrian people.
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."