Members of a Syrian pro-regime militia gunned down seven Sunni men working on reconciliation in the central province of Homs overnight, the Syrian Observatory for Human Rights said on Tuesday.
"Seven men belonging to a reconciliation committee, including two retired officers and the imam of a mosque in the town of Zara... were killed yesterday by members of the People's Committee," the group said, referring to a pro-regime armed group.
Regime-authorised reconciliation teams have sprung up across Syria, working on grassroots mediation and negotiated truces in various areas.
The team targeted on Monday had successfully mediated before, the Observatory said, and was working to smooth ties between Sunnis and Alawites in religiously-mixed Homs.
Many Syrian Sunnis back the Sunni-led uprising against President Bashar al-Assad, who is Alawite and the conflict has led to increasing sectarian tensions in the country, particularly in Homs.
The Observatory said the group of mediators was on their way to a meeting in the town of Tal Kalakh.
They were killed at the entrance to the Alawite village of Hajar al-Abyad, which the Observatory described as "one of the most important strongholds for the shabiha (pro-regime militants) in the region".
The group distributed a video showing black body bags tagged with pieces of paper bearing each man's name.
Elsewhere, the Observatory reported, nine Syrians, including a child, were executed by regime forces at a checkpoint in Damascus province on Monday.
"Nine citizens, including a child, were shot dead by regime forces near the town of Qara, in the Qalamun area of Damascus province, yesterday (Monday) evening," the group said.
The nine were "executed" at a military checkpoint in the area, the group said, citing local activists.
Video footage shot by activists and distributed by the Observatory showed bodies lain out on the white floor of a room, some of them partially covered with a piece of white plastic sheeting.
Several appeared to have been shot in the head, and others in the chest.
More than 100,000 people have been killed in Syria since an uprising erupted against the rule of Assad in March 2011, according to the Observatory's figures.