Amman/Aleppo: A Syrian military helicopter crashed in flames under rebel fire in Damascus on Monday, and a government warplane fired rockets at targets on the capital's outskirts for what rebels said was the first time.
The focus of fighting appears to have returned to the outskirts of capital after weeks of battles centred on the northern city of Aleppo.
Opposition activists said at least 62 people had been killed in the assault on suburbs of Damascus on Monday, some summarily executed, a day after they accused Assad's troops and sectarian militia of massacring hundreds of people in the neighbouring town of Daraya.
The focus of fighting appears to have returned to the outskirts of capital after weeks of battles centred on Aleppo.
At the United Nations, Secretary-General Ban Ki-moon condemned the Daraya killings as "an appalling and brutal crime" that should be independently investigated immediately.
State television confirmed a helicopter had crashed in Damascus but gave no details. Opposition activists said rebels had shot it down; opposition video footage showed a crippled aircraft burning up and crashing into a built-up area, sending up a pillar of oily black smoke.
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."
Video footage carried the sound of people celebrating the helicopter's dive with shouts of "Allahu akbar" (God is great).
Although rebel commanders have asked foreign governments for anti-aircraft missiles, Western nations are unwilling to supply such weapons for fear of them falling into hostile hands. There was no indication fighters in Damascus had used any missiles.
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 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.
Syrian authorities have banned entry to most foreign media, making it impossible to verify accounts by activists and residents of activity in the capital.
Army helicopters had been rocketing and strafing crowded working class suburbs on the eastern outskirts of the city since Sunday. "The sound of gunfire and mortar shells exploding hasn't stopped," an opposition activist, Samir al-Shami, said from the area. "I see smoke rising everywhere."
Video from campaigners showed 20 bodies on the floor of a mosque, including three children.
On Sunday, opposition activists said they had found about 320 bodies, including some of women and children, in Daraya, just southwest of Damascus. Most had been killed execution-style, they said. Videos on the Internet showed rows of bodies wrapped in sheets. Most seemed to be young men, but at least one video showed several children who appeared to have been shot in the head. The body of one toddler was soaked in blood.
At the United Nations, Ban demanded an investigation.
"The secretary-general is certainly shocked by those reports and he strongly condemns this appalling and brutal crime," Ban's spokesman Martin Nesirky said. "This needs to be investigated immediately, in an independent and impartial fashion."
Highest daily toll
The uprising, which began as peaceful protests, has become a civil war. U.N. investigators have accused both sides of war crimes but laid more blame on government troops and pro-government militia than on the rebels.
The killings in Daraya, a working class Sunni Muslim town that sustained three days of bombardment before being overrun by the army on Friday, pushed the daily death toll to 440 people on Saturday, one of the highest since the uprising began, an activist network called the Local Coordination Committees said.
The official state news agency said: "Our heroic armed forces cleansed Daraya from remnants of armed terrorist groups who committed crimes against the sons of the town."
In Paris, French President Francois Hollande warned Assad that any use of chemical weapons would be a legitimate justification for military intervention. The United States and Britain have made similar warnings.
"With our partners we remain very vigilant regarding preventing the use of chemical weapons, which for the international community would be a legitimate reason for direct intervention," Hollande said in a speech.
Clashes are raging across Syria as the rebellion grows increasingly bloody, particularly in Aleppo, Syria's biggest city and its economic hub, where the army and rebels appear stuck in a war of attrition.
Fighting in the northern city on Sunday was the heaviest in the past week, according to Reuters journalists there. Helicopters were circling and firing occasionally on Monday.
Reuters journalists saw a fighter jet fire on an eastern neighbourhood of the city for two hours. Activists said southern districts of Aleppo were also repeatedly attacked on Monday.
"The front line has not changed. We cannot progress due to a lack of ammunition," said Abu Walid, a rebel commander in Aleppo. "All we can do is hold our positions."
Rebels say they control at least half the city of 2.5 million, but their hold is fragile since Assad's forces can unleash their air power and artillery.
The United Nations says more than 18,000 people have been killed in the conflict that pits a mainly Sunni opposition against a ruling system dominated by the Assad family and other members of the Alawite faith, an offshoot of Shi'ite Islam.
Diplomatic efforts to stop the violence in Syria are stalled by a stalemate between Western countries, Sunni-led Gulf Arab states and Turkey - which all support the opposition - and Shi'ite Iran, which backs Assad, as do Russia and China.
In Ankara, Turkish Foreign Minister Ahmet Davutoglu called for more help from other countries with a growing Syrian refugee crisis and said Ankara would stress this at a U.N. Security Council meeting on Syria later this week.
The number of Syrian refugees in Turkey has nearly doubled over the past two months to more than 80,000 and Turkey has begun temporarily holding thousands of people on the border while they scrambled to erect shelters.
"On the one hand, for the sake of our brotherhood with the Syrians we want to carry out our humanitarian duty, but there is a burden brought about by the numbers. This burden must be shared by the international community," Davutoglu said.