Syrian state media has reported that government troops have killed 175 rebel fighters in an ambush south of the capital, Damascus.
The SANA news agency said on Wednesday that the attack happened at dawn in the opposition-held area of eastern Ghouta.
According to the report, an army unit "spotted Jabhat al-Nusra and Liwa al-Islam terrorists" near Damascus, and "killed 175 of them and wounded several others".
Saudis, Qataris and Chechens were reportedly among the dead, according to SANA. Al Jazeera cannot independently verify the nationalities of those killed.
The attack, apparently the deadliest against the rebels for months, took place in the key rebel stronghold targeted in a chemical attack in August 2013 that killed hundreds of people.
The Syrian Observatory for Human Rights, a group based in the UK which has a network of contacts inside Syria, told the AFP news agency that dozens were killed in the ambush.
"Dozens of Islamist fighters were killed and wounded in an ambush by loyalist troops, with the help of Hezbollah, near Otaybeh village in the Eastern Ghouta area," it said.
Another 10 armed fighters were also reportedly taken as prisoners.
Activists told Al Jazeera that the fighters were killed while trying to cross from the eastern side of Damascus to Adra north of Damascus, using "a risky road" because of the siege.
Syrian state television had earlier reported "dozens" killed, mostly non-Syrians, in a "well-organised ambush" following a tip-off.
Lebanon-based Al-Mayadeen TV station showed dozens of bodies scattered along an unpaved road.
Syria's war has killed more than 140,000 people since March 2011.
According to the United Nations on Wednesday, there have been two and a half million Syrians who have fled the country, with the number expected to exceed four million by the end of 2014.