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The Observatory confirmed the ambush in Adra, saying 49 rebels were killed. It said an elite Republican Guard officer who led the ambush also was killed.

Also Sunday, activists reported rare fighting between rebels and regime forces in the coastal province of Tartus, a stronghold of Mr. Assad’s minority Alawite sect.

The Observatory accused the regime of killing 13 members of the same family, including four women and six children, in an attack in the Sunni Muslim village of Bayda following the clashes. The village is predominantly Sunni but is located in the Alawite ancestral heartland. It was the site of a mass killing in May.

Syrian state television claimed that a pro-government group had hacked into two social messaging networks and seized records of local users.

The hacking could expose Syrian rebels and other activists who depend on the networks to publicize army crackdowns on their hometowns and communicate with each other. Many telephone landlines and cellphones in Syria are assumed to be tapped.

The TV said the social networking site Tango was hacked on Sunday by the Syrian Electronic Army, a shadowy group that supports Mr. Assad’s regime.

Tango confirmed in a statement that it had experienced “cyber intrusion that resulted in a brief, unauthorized access to some data on Friday. Increased security protocols are now in place.”

Syrian media said another network, Truecaller, also was hacked last week.

A spokesman for the company, Kim Fai Kok, confirmed that Truecaller’s website had been hacked, but the hackers only got hold of so-called tokens that don’t contain any information that can identify users. Ms. Fai Kok said the company has been able to trace the hacker attack to Syria and now has taken extra measures to improve the security of its services.

• Zeina Karam reported from Beirut. Associated Press writer Malin Rising in Stockholm contributed to this article.