Two people have been killed in eastern Syria after police opened fire on a crowd who came out to welcome UN ceasefire observers, according to a rebel official.
There was no independent confirmation of Tuesday's incident in the province of Deir al-Zor.
"As soon as the UN convoy entered Al-Busaira, a jubilant crowd of hundreds came out to welcome them. It was not minutes before they came under fire," Abu Laila, a Free Syrian Army (FSA) official, said by phone from the town.
"The observers immediately left Al-Busaira. We called them to come back but they refused."
Fighting ensued between President Bashar al-Assad's forces and FSA fighters based in the town, Abu Laila said.
Another opposition source in Deir al-Zor said that government forces surrounding Al-Busaira began firing anti-aircraft guns at the town.
The reports of violence come three days after a suicide attack hit the main town of in Deir al-Zor, killing at least seven people and wounding 100 others, according to a Syrian foreign ministry spokesman.
Government troops have been battling a widening uprising against Assad for 14 months.
In-depth coverage of escalating violence across Syria
Al-Busaira is one of many towns and villages under rebel control in Deir al-Zor, a large oil-producing province bordering Iraq, that have been attacked repeatedly in the last four months by government troops trying to regain control.
Assad, a member of Syria's Alawite minority, had relied on a network of alliances with Sunni Muslim tribes forged by his late father, Hafez al-Assad, to keep Deir al-Zor under control.
But these understandings began breaking down after the province erupted in mass demonstrations in July demanding Assad's removal, and tanks were sent to quell the protest movement.
There are 257 unarmed United Nations observers in Syria, sent to enforce an internationally brokered ceasefire that has been regularly violated by Assad's forces and rebels.