Fighting between rebels and President Bashar al-Assad's forces erupted in an oil producing province in eastern Syria on the eve of a parliamentary election.
Rebels armed with rocket-propelled grenades attacked tank positions in the east of the provincial capital Deir al-Zor.
Witnesses and opposition sources say that the army still has tanks and heavy weapons in cities and towns in violation of a ceasefire being monitored by a UN team.
Reports from Syria cannot be independently verified as state authorities have barred international journalists and rights groups.
Rebels are continuing their guerrilla attacks on military convoys and army roadblocks that have cut off swathes of the country, according to witnesses and opposition sources.
50 out of a planned total of 300 UN observers are now in Syria to monitor the ceasefire declared on 12 April, but their presence has not halted 14 months of violence.
The authorities say they are fighting what they call foreign backed terrorists in Deir al-Zor and across the country who are bent on sabotaging what state media describe as a comprehensive reform programme being led by Assad that is more advanced than in Western democracies.
The authorities are touting tomorrow's parliamentary election as a showcase of these reforms.
However, the opposition says it will change little in a rubberstamp assembly that has been chosen by the ruling Assad family, backed by the powerful secret police, for the past four decades.