Activists say Syrian fighter jets made rare sorties on the outskirts of the capital, Damascus, killing at least 60 people in its eastern suburbs, the same day a Syrian military helicopter crashed while under rebel fire.
They said aerial attacks by at least two fighter jets late on Monday targeted the neighbourhood of Zamalka, and the more easterly suburb of Saqba, where Free Syrian Army fighters had attacked and overrun several army checkpoints earlier in the day.
Both suburbs are poor and inhabited predominantly by Sunni Muslims, who make up the majority of Syria's population and have been at the forefront of the fighting against Bashar al-Assad, Syria's president.
Video footage seen by a Reuters news agency reporter of the aftermath of an attack by one of the jets firing rockets at an apartment building showed people running away with their children and the six-storey building collapsing like an accordion.
Monday's air raids came as Turkish officials say up to 10,000 Syrians are waiting on the Syrian side of the border while Turkey rushes to build more camps to accommodate the influx and carries out more stringent security checks on the newcomers.
Clashes return to Damascus
The focus of the 17-month struggle appears to have returned to the outskirts of Damascus after weeks of battles centred on the northern city of Aleppo.
Activists also reported that a bombing in a Damascus suburb on Monday night, which killed two people, described as regime loyalists; and an improvised explosive device that went off in the suburb of Jaramana, injuring several.
Opposition activists said at least 62 people were killed in an assault on the suburbs of Damascus on Monday, some summarily executed.
The crackdown occurred a day after they accused Assad's troops and pro-government militias of massacring hundreds of people in the neighbouring town of Daraya.
At the UN, Ban Ki-moon, the secretary-general, condemned the Daraya killings as "an appalling and brutal crime" that should be independently investigated immediately.
Egypt's President Mohamed Mursi, preparing to make his debut on the stage of world diplomacy, called on Monday for Assad's allies to help push the Syrian leader out of power.
"Now is the time to stop this bloodshed and for the Syrian people to regain their full rights, and for this regime that kills its people to disappear from the scene," he told Reuters in his first interview with an international news organisation before embarking on a trip to China and Iran.
"There is no room to talk about reform, but the discussion is about change," Mursi said.
Syria's state television confirmed that a helicopter had crashed in Damascus on Monday but gave no further details.
Opposition activists said rebels had shot it down; video footage showed a crippled aircraft burning up and crashing into a built-up area, sending up a pillar of black smoke.
In-depth coverage of escalating violence across Syria
The possible shooting down of the helicopter, the latest of several such successes claimed by lightly armed rebel fighters, bolstered morale in their 17-month struggle battle to bring down Assad.
However, even more intense army bombardments followed the helicopter crash, witnesses said.
"It was flying over the eastern part of the city and firing all morning," an activist calling himself Abu Bakr told Reuters from near where the helicopter came down in the eastern suburbs. "The rebels had been trying to hit it for about an hour," he said. "Finally they did."
Activists said 11 of Monday's dead were killed in the district of Jobar, where the helicopter came down. Five of the Jobar victims had been captured and summarily executed by security forces, and the others died when their homes were hit.
Later footage showed a fighter jet swooping on a built-up area. An explosion is heard and a voice says: "It is firing rockets." Activists said it had struck targets on the eastern outskirts of the capital.
"This is the first time a warplane strikes the edges of Damascus," a Damascus-based activist told Reuters by Skype. "This plane was swooping over the area all afternoon."
Activists said that at least two fighter jets had caused the casualties in the eastern suburbs.
Turkish camps full
The surge in fighting around Damascus comes amid reports that all nine Turkish refugee camps along the border with Syria are full. Turkey has so far taken in more than 80,000 Syrian refugees.
Until recently, newcomers were being housed in schools, dormitories or sports centres near the border while Turkish authorities tried to construct four new camps that will increase Turkey's capacity to 100,000 refugees.
The refugees still stuck on the Syrian side will be allowed in "within a day or two" when a new camp near the border becomes operational, a Turkish official said on Monday.
Turkey's Red Crescent organisation was providing emergency aid to the refugees as they wait to cross into Turkey, the official said.
Another official said Turkey was also carrying out more stringent security checks on the refugees, adding to the delay in bringing them across the border.
The tighter checks come amid Turkish fears that Kurdish fighters in southeast Turkey may be coming in through Syria.
There are also concerns that foreign jihadists are moving in and out of Turkey to fight the Assad government.
Ahmet Davutoglu, Turkey's foreign minister, has said the UN should establish refugee camps inside Syria and that his country would struggle to cope if the refugee numbers rise substantially.
"Turkey is carrying out its humanitarian duties towards the Syrian people with whom it has historic brotherly ties," Davutoglu said on Monday.
"On the other hand, the increasing numbers are becoming an encumbrance. The international community must help share this burden."