The Syrian Observatory for Human Rights said fighting was continuing on Saturday in Wadi Barada, a rebel-held district northwest of Damascus that is home to the capital’s main water source.
The Britain-based monitor said the overnight fighting had killed at least seven Syrian soldiers and wounded around 20 others, some of whom were in serious condition.
Two civilians were also killed in the violence, the group said.
Water supplies from Wadi Barada have been cut since December 22.
The regime and the rebels have traded accusations of responsibility, with the government saying the rebels deliberately targeted water infrastructure and the opposition saying army strikes hit pumping facilities.
Fighting has continued in the area despite the start on December 30 of a nationwide truce brokered by regime ally Russia and opposition backer Turkey.
The ceasefire, accepted by both the government and key rebel groups, has brought quiet to large parts of Syria, but the violence has continued in Wadi Barada.
There have been discussions about the possibility of an agreement to end the fighting, with experts able to enter the area to fix the damaged water infrastructure.
But so far no deal has been reached, and the UN warned earlier this week that 5.5 million people were now affected by water shortages in the capital and its suburbs.
More than 310,000 people have been killed in Syria since the conflict began with anti-government protests in March 2011. Over half the country’s population has been displaced.
PTI