The death of 130 rebels and civilians was an execution carried out by the Syrian government and its Shiite allies, alleged Syria's opposition Free Syrian Army Saturday.
They were killed in the town of al-Ziyabiya amid battles to control southern Damascus suburbs, which began two days ago.
"The army of (Syrian President Bashar) Assad and their agents - the Iranian militia of Hezbollah and some Iraqi Shiites loyal to Tehran - have executed 130 men in areas near al-Ziyabiya," FSA spokesman Louay Mokdad said.
"We call on the world community to immediately look into this new massacre committed by the tyrant regime of al-Assad," Mokdad told DPA by phone.
The state-run SANA news agency reported that government forces managed to fully control al-Ziyabiya and had killed many "terrorists at the outskirts of the Bouayda suburb."
The report added that the armed forces continued to advance towards Bouayda and Hujeira in a move aimed at "cleansing the area from terrorists," a term used by the regime to identify opposition fighters.
Rami Abdel-Rahman, head of the opposition watchdog Syrian Observatory for Human Rights, said "we have information that there were some fighters and people trapped inside al-Ziyabiya, as the Syrian army were storming the area, but we still know nothing about their fate."
State television showed pictures of what it claimed was ammunition "left by the dead terrorists" in the area of Sheikh Omar, between al-Ziyabiya and Bouayda.
An army source told SANA that restoring security and stability in the towns of Husseiniya and al-Ziyabiya "will tighten the grip on the terrorists, who are still hauled up in Bouayda and Hujeira".
Meanwhile Saturday, Al-Qaida leader Ayman Zawahri urged jihadis in Syria to unite, an appeal likely aimed at rival affiliates of his terror network fighting there to oust Assad.
Zawahri says fighters must "rise above organizational loyalties and party partisanship" and unite behind the goal of setting up an Islamic state.
However, he suggests he will not impose unity, saying in an audio message Friday that "what you agree upon will also be our choice."
Two Al-Qaida-linked groups have emerged in Syria's civil war — Jabhat Nusra and the Islamic State of Iraq and al-Sham. The first is commanded by a Syrian, the second by an Iraqi, but both are loyal to Zawahri.
Zawahri also urged Syrian regime opponents not cut deals with Westerns and secular groups.
More than 100,000 people have been killed in the conflict, which began in March 2011 with anti-government protests, according to the United Nations.
Want to enjoy 'Zen' reading - with no ads and just the article? Subscribe todaySubscribe now