Syrian rebels seized several parts of a suburb of the capital Damascus on Saturday, activists said, and heavy fighting continued late into the night.
The Syrian Observatory for Human Rights said insurgents were now fighting the army at the entrances to the suburb of Douma, which has been a centre of protests in the 10-month revolt against President Bashar Assad.
"No one can get in or out of Douma right now. This is the first time the rebels do anything more than hit-and-run attacks. Tonight they started making barriers in the streets and every few minutes I hear gunfire and explosions," an activist living in Douma told Reuters by Skype.
The rebel victory came hours after bomb blasts killed 14 prisoners traveling in a security vehicle in northwest Syria on Saturday, the state news agency said, and troops fought rebels elsewhere as the Arab League weighed whether to keep monitors in place.
Syria's SANA agency said a "terrorist" group had set off two explosions that also wounded 26 prisoners, as well as six police guards. It said the assailants had also attacked ambulances sent to the scene, on the road between the towns of Idlib and Ariha.
The British-based Syrian Observatory for Human Rights, which tracks the 10-month-old revolt against President Bashar Assad, had earlier reported the attack in northwestern Idlib province.
It said army troops were clashing with soldiers who have deserted and joined an anti-Assad insurgency in the Jebel al-Zawiya region of Idlib, which is near the Turkish border.
Al Jazeera television said army troops and deserters were also battling in the northwestern city of Jisr al-Shughour.
In a separate incident, at least 23 people were killed in the Syrian province of Idlib near the border with Turkey, opposition activists said.
"At least nine people, mainly (army) defectors, were killed in clashes between government forces and deserters in Idlib," Abu Omar, a Syrian activist, told dpa by phone.
The Arab League looks set to extend its monitoring mission in Syria, given the lack of any Arab or world consensus on how to halt bloodshed there, an Arab diplomatic source said.
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