At least 16 Syrian soldiers were killed Saturday in a car bomb and fighting that followed at a checkpoint in a Damascus suburb.
Syrian state media blamed the explosion on "terrorists," the BBC reported.
Also on Saturday, United Nations humanitarian chief Valerie Amos has called for an "immediate pause in hostilities" in Damascus' rebel-held suburb Moadamiyah.
Amos said 3,000 people were trapped in the town amid intense fighting.
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In other developments, nine Lebanese Shiite pilgrims kidnapped by rebels in Syria last year have been released and are back in Beirut after being an international prisoner swap that secured the release of two Turkish pilots kidnapped by Lebanese gunmen.
Two Turkish pilots arrived safely back in Istanbul Saturday evening.
The Syrian Observatory for Human Rights said rebels led by the al-Qaeda-linked Jabhat al-Nusra, or Nusra Front, carried out the suicide bombing while trying to capture the checkpoint in the mainly-Christian area of Jaramana.
The attack triggered several clashes between rebels and Syrian troops.
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Rebels fired rockets into Jaramana, which is still held by the government, and Syrian fighter jets responded by striking parts of the city held by opposition forces, according to UPI.
Lebanon's Interior Minister Marwan Charbel told AFP the nine Lebanese pilgrims had been freed by rebels forces and were on their way to Turkey.
Their release comes after a senior Lebanese security official travelled to Damascus to discuss a prisoner exchange deal. After the pilgrims were released, the two Turkish pilots kidnapped as retribution also were freed, according to Al Arabiya.
"Very favourable developments are under way concerning the two Turkish pilots. This matter has been largely settled," Turkish Foreign Minister Ahmet Davutoglu said earlier on local television, adding that the men could be freed "within hours or days."