Syrian rebel fighters killed 12 members of a pro-regime militia during clashes overnight in the central city of Homs, and troops responded by shelling them on Friday, monitors said.
The Syrian Observatory for Human Rights also reported that, elsewhere, shells hit the Sayyida Zeinab shrine, a Shiite Muslim pilgrimage site on the outskirts of Damascus, killing at least one person.
"Twelve members of the pro-regime People's Committees were killed... during fighting with rebel forces on the outskirts of the Khaldiyeh neighbourhood," the group said.
The rebel-held district is one of several regime forces have laid siege to for more than a year.
The regime has increasingly used militia groups to bolster its regular forces in battles against rebel fighters seeking to overthrow President Bashar al-Assad.
The Observatory, which relies on a network of activists, doctors and lawyers on the ground, said government troops were continuing to shell the neighbourhood on Friday.
In Damascus province, meanwhile, the top administrator of the Sayyida Zeinab shrine was killed in shelling of the holy site, the Observatory said.
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The shelling hit the compound of the shrine, which is home to the mausoleum of Sayyida Zeinab, granddaughter of the Prophet Mohammed and particularly revered by Shiites.
In northeastern province of Hassakeh, clashes raged between Kurdish fighters and jihadists from the Al-Qaeda-affiliated Al-Nusra Front and Islamic State of Iraq and the Levant.
The Observatory said a Nusra fighter blew himself up near the headquarters of the Kurdish YPG brigade, which has in recent days pushed jihadist fighters out of the town of Ras al-Ain.
In western Tartus, three members of the Communist Labour Party who also belong to the National Coordination Body for Democratic Change -- Syria's internal opposition -- were arrested at a political security checkpoint.
The committee, in a statement, identified those arrested as Christian painter Yousef Abdelki, 62, Alawite Tawfiq Omran, and Druze Adnan al-Dibs.
The head of the Communist Labour Party, Alawite Abdel Aziz al-Khayer, was arrested in Syria in September 2012.
At least 135 people were killed in violence across Syria on Thursday, the group said, adding to its overall toll of more than 100,000 dead since the country's uprising flared in March 2011.