Rights activists say Syrian army defectors killed seven government security force members while ambushing a patrol following an army raid that cost 11 civilian lives earlier Tuesday.

The London-based Syrian Observatory for Human Rights says both incidents took place in Idlib province, a restive area that borders Turkey. The observatory and other groups report that security forces and pro-government “shabiha” militiamen swept through villages and attacked infiltrators at the border, wounding dozens.

The Associated Press, quoting activists, reports a senior Syrian officer was killed in a retaliatory ambush by anti-regime fighters. Syrian state-run media also reported that border guards clashed with a group of 15 “terrorists” attempting to enter the country from Turkey, killing two of them.

About 7,500 Syrians have fled across the Turkish border to escape the brutal government crackdown.

U.N. human rights chief Navi Pillay said Monday her office has received credible reports from a variety of sources indicating the Syrian death toll since unrest began in March “probably exceeds 5,000.”

She released the statement shortly after a meeting with U.N. Security Council representatives in New York, where she said the violence should be examined by the International Criminal Court.

Pillay also warned that sources fear a major assault on the flashpoint city of Homs may be imminent.

Syria's uprising has turned increasingly violent in recent months, with defecting soldiers fighting back against the army and once-peaceful protesters taking up arms to protect themselves.

A general strike continued for a third day Tuesday in several regions across Syria as activists push for an end to Mr. Assad's rule through a campaign of civil disobedience.