Syrian army troops have killed 175 opposition fighters, many of them linked to al-Qaeda-linked groups, in an ambush described as one of the deadliest attacks by government forces near Damascus, according to state media.
An opposition group alleged that Wednesday dawn's ambush was carried out by the Lebanese Hezbollah group, which has been instrumental in helping President Bashar al-Assad's regime push back rebels entrenched in the suburbs of the Syrian capital.
Syrian state news agency SANA quoted a field commander in the Eastern Ghouta area as saying most of the rebels killed in the assault near Oteibah lake, southeast of Damascus, belonged to the al-Qaeda-linked Nusra Front.
The report claimed several of those killed were foreign fighters who came to Syria from Saudi Arabia, Chechnya and Qatar.
In-depth coverage of escalating violence across Syria
The agency posted several photographs on its website showing dozens of bodies of men, some with leg wounds, lying in a dirt track of an open field.
Some were wearing fatigues, but most wore civilian clothes and appeared to have been carrying bags of clothes and bottles of water that were scattered on the ground.
Activists told Al Jazeera the fighters were killed while trying to cross from the eastern side of Damascus to Adra, north of the city, using "a risky road" because of an ongoing government siege.
The Britain-based Syrian Observatory for Human Rights said at least 152 opposition fighters were killed, most of them Nusra Front and other fighters from allied brigades.
Reinforcing that report, Hezbollah's Al-Manar TV aired exclusive footage of what it said was the ambush, showing at least two large bombs that were detonated along the route used by the opposition fighters.
An army colonel told the Lebanon-based Al-Mayadeen channel that his troops acted on intelligence and the rebels lost "more than 150 men".
Syria's pro-government Al-Ikhbariya channel aired its own footage of the aftermath, showing soldiers milling about as dozens of bodies of rebels lay scattered on the ground.
The station also broadcast images of what it said were rebels' weapons, confiscated by the army.
Delegates' kin arrested
In another development, a US administration official said on Wednesday that the Syrian regime had arrested relatives of the opposition's delegation to the peace talks in Geneva earlier this month.
The US was "outraged" by reports that the Syrian government "has arrested family members of the Syrian opposition coalition delegation to the Geneva II peace talks, designated delegates as terrorists, and seized delegates' assets," Jen Psaki, State Department spokeswoman, said.
"We call on the regime to immediately and unconditionally release all those unfairly arrested."
Among those held was Mahmoud Sabra, the brother of Geneva delegation member Mohammed Sabra.
Through such actions the Syrian regime was "not only defying the international community but also seeking to suppress the legitimate aspirations of the Syrian people", Psaki said.
A second round of the UN-led talks in the Swiss city, dubbed Geneva II, broke down in acrimony on February 15, only weeks after the rival parties sat down in January for the first time in the three-year civil war to seek a political settlement.
So far no date has been set for the talks to resume.
Meanwhile, in Damascus, Assad held talks on Alaeddin Boroujerdi, head of the influential Iranian parliamentary committee on national security and foreign policy.
Later Bouroujerdi said he discussed the latest military developments with Syrian officials.
Also on Wednesday, the international mission to rid Syria of its chemical weapons by June 30 said that a batch of sulphur mustard, widely known as mustard gas, was shipped out of the country.
Sigrid Kaag, head of the joint operation by the UN and the Organisation for the Prohibition of Chemical Weapons, called for Syria to continue its efforts to relinquish its arsenal "in a safe, secure and timely manner, through systematic, predictable and high-volume movements".
The mission to eliminate Syria's chemical stockpile said the Assad government has missed at least two deadlines in the past two months to remove chemicals.
Separately, Chris Gunness of the UNRWA relief agency said a humanitarian team was permitted to work from one of its facilities in Yarmouk, a besieged Palestinian district of Damascus, for the first time since December 2012.
He called this "a highly encouraging step towards re-establishing full services and humanitarian access to Yarmouk" and said 450 food parcels were distributed "without the involvement of third parties".
Yarmouk refugee camp, which houses about 18,000 Palestinians and an unknown number of Syrians, has seen some of the worst fighting in the capital, leading to severe food shortages and widespread hunger.
More than 100 people have died in camp of starvation and hunger-related illnesses, according to the UN.