BEIRUT — Pro-government gunmen have kidnapped more than 300 people in northwestern Syria in retaliation for the abduction of 42 Shiite Muslims this week, an activist group said Saturday.

The tit-for-tat kidnappings point to the dark sectarian overtones of Syria’s civil war, which pits a predominantly Sunni Muslim rebellion against a regime dominated by President Bashar Assad’s minority Alawite sect, an offshoot of Shiite Islam. The country is also home to Christian, Kurdish, Armenian and Shiite communities.

The Britain-based Syrian Observatory for Human Rights said the spate of kidnappings this week took place in the northern province of Idlib, which borders Turkey.

Kidnapping for ransom has been widespread across Syria since the crisis began in March 2011, but sectarian and political abductions have been rare.

The Observatory said the 42 Shiites, mainly women and children, were snatched Thursday from a bus traveling from the Shiite villages of Foua and Kfarya to the capital Damascus. Observatory director Rami Abdul-Rahman, said it was not clear who took them, adding that Shiites have refused to give details.

In retaliation for the bus kidnappings, members of the pro-government Popular Committees set up a checkpoint around the two Shiite villages and on Thursday and Friday were taking people from cars they stopped, the Observatory said. It added that most of the people abducted were from the Sunni villages of Saraqeb, Binnish, Sarmin, Qimnas, Maaret al-Numan and Maaret Musreen.