Deadly clashes raged on the edge of Damascus and rival rebel factions battled each other in northern Syria as international chemical weapons inspectors began to secure sites where they will work.
Wednesday's fighting underscored the immense security challenge that the dozens of disarmament experts must negotiate as they work amid the civil war to meet tight deadlines for eliminating President Bashar al-Assad's estimated 1,000-tonne arsenal of chemical weapons.
In northern Damascus, fierce clashes between Syrian troops and al-Qaeda-linked fighters had killed at least 19 soldiers and pro-government militiamen in the past three days, according to the Britain-based Syrian Observatory for Human Rights.
The rebels, mostly fighters from the ranks of the al-Qaeda-linked Jabhat al-Nusra, also sustained losses, but did not disclose them, the observatory said. It also noted clashes in Jobar on the capital's eastern edge.
In Syria's north, the observatory reported clashes between al-Qaeda rebels and more moderate groups in the town of Azaz on the Turkish border. Militants from the Islamic State of Iraq and the Levant made advances against fighters from the Western-backed Free Syrian Army. There were no reports of casualties.
The weapons inspectors' mission - endorsed by a UN Security Council resolution passed last week - is to scrap Syria's capacity to manufacture chemical weapons by November 1 and destroy its entire stockpile by mid-2014.
A convoy of SUVs with UN markings departed the central Damascus hotel where the team from the Organisation for the Prohibition of Chemical Weapons is staying as the inspectors headed out on Wednesday for their first full day in the country.