At least 70 people have been killed by an air strike on a petrol station in the outskirts of the Syrian capital, Damascus, activists say.
Damascus residents say they saw burning bodies and horrific scenes after the air strike in Mleiha district.
Unverified reports from activists suggested 70 people had been killed.
The UN’s Human Rights Council said a new study suggested more than 60,000 had died since the start of the unrest, many more than activists have claimed.
UN rights chief Navi Pillay said in a statement that the number of casualties was “truly shocking”.
Activists posted video footage online purporting to show the latest air strike.
It featured charred bodies and burnt-out vehicles.
The reported death toll ranged from about 30 to 70. The figures could not be verified.
At least 70 people have been killed by an air strike on a petrol station in the outskirts of the Syrian capital, Damascus, activists say
One activist told Reuters news agency that the warplane had attacked the petrol station as a consignment of fuel arrived.
Mleiha is not an opposition stronghold, and civilians appear to have borne the brunt of the attack.
Many of the killed or injured are women and children.
Syria is in the grip of chronic fuel shortages, and motorists often wait for hours in queues at petrol stations.
Activists told the Associated Press that a single missile had struck the station.
The strike sparked a huge explosion that engulfed vehicles that had been waiting in line.
Navi Pillay said an “exhaustive” study of all deaths between 15 March 2011 and 30 November 2012 showed 59,648 had been killed between those dates.
“Given there has been no let-up in the conflict since the end of November, we can assume that more than 60,000 people have been killed by the beginning of 2013,” she said.
The Syrian Observatory for Human Rights, a UK-based activist group, had put the figure at 44,000.
A warplane has attacked a petrol station in the north-east of Syria, killing at least 30 people, opposition activists say.
A rebel group said people had been queuing for petrol and diesel near Ain Issa at the time.
The village is some 20 miles (32 km) from the Tal al-Abyad border post, seized by rebels on Wednesday after a lengthy battle with government forces.
The number of casualties was expected to rise, reports said.
Unverified footage posted online showed several charred vehicles and one activist group said 70 wounded people had been taken to hospital in the nearby town of Raqqa.
A warplane has attacked a petrol station in the north-east of Syria, killing at least 30 people
One activist told AFP news agency that the filling station was the only one still operating in the area and had been crowded at the time of the explosion.
A barrel of explosives was dropped on the petrol station, opposition activists said, causing a huge explosion and fire.
Syria’s armed forces have exploited their air power in recent weeks.
The use of hugely destructive but crude bombs involving a barrel packed with explosives has become increasingly common.
It is often impossible to verify the circumstances and the extent of casualties involved in attacks in Syria because reporters are unable to travel around the country.
But the burned-out pick-up trucks and a smouldering tractor seen in the video indicated a recent attack.
A day after the Tal al-Abyad border post was seized by Free Syrian Army rebels, opposition groups reported that fierce clashes between government and rebel forces were still going on for control of security buildings in the town.
The crossing-point is on the main road between Raqqa and the Turkish town of Sanliurfa and Turkish officials told AFP news agency that pro-Assad forces were shelling the area in an attempt to recapture the post.
Turkish media showed images of the rebel flag flying at the crossing alongside the Turkish flag.
Local schools in the Turkish border town of Akcakale were closed because of the danger of stray bullets and AFP reported that three Turkish civilians had been wounded.
There were conflicting reports earlier when a military helicopter was said to have crashed in the suburb of Douma, north-east of the capital, Damascus.
Syrian state media reported that the helicopter’s rotor had clipped the tail of a Syrian Arab Airlines plane carrying 200 passengers. The plane was then said to have landed safely at Damascus airport.
All passengers on board the plane were unharmed, reports said.
Initially, opposition activist group the Syrian Observatory for Human Rights said rebels had shot down the helicopter but that claim was not repeated elsewhere.
The government has increasingly used helicopters and planes in its fight against the rebels and activists reported clashes in the Douma area at the time.
Last month, rebels said they shot down a helicopter on the outskirts of Damascus.
Clashes were reported on Thursday across Syria, including Damascus and the second city, Aleppo.
Government forces were said to have overrun several districts in the south of Damascus where rebels have been holding out.
Syrian state TV said at least 100 “terrorists” were detained in the densely populated Yarmouk area, an unofficial Palestinian refugee settlement.
In the Dutch political capital, The Hague, a group of financial experts, foreign diplomats and Syrian defectors was meeting to look for new economic ways of weakening Syrian President Bashar al-Assad’s grip on power.
The group, called the Friends of Syria, was discussing how to make sanctions on the Syrian government more effective and how to track down the Assad government’s hidden financial assets.
Dutch Foreign Minister Uri Rosenthal at the meeting said that one of the problems was that not all countries implemented sanctions on Syria.
Abdo Husameddin, a former Syrian oil minister who defected from the regime in March, said President Bashar al-Assad’s extended family may have billions of dollars hidden abroad.
“They are talking about probably more than $10 billion. And there are some other faces in fact hidden beside the regime itself. So all of this money is not directly under the name of Assad himself, but by other names.”
On Wednesday, the foreign minister of Iran, Syria’s close regional ally, held talks with President Bashar al-Assad, who told him that the attack his country was facing was not just against Syria, but also against its alliance with Iran and Hezbollah.
The UN estimates that the conflict has left at least 20,000 people dead.