Syrian engineers were expected to carry out urgent maintenance Wednesday (March 29th) on the country's largest dam, where the Syrian Democratic Forces (SDF) have been battling the "Islamic State of Iraq and the Levant" (ISIL), which still controls most of it, AFP reported.

The maintenance work, which entails opening a spillway to relieve the pressure of water on the dam, will involve the engineers entering areas held by ISIL, a technician inside the complex said.

The fighting between the SDF and ISIL has raised fears for the integrity of Tabqa Dam, which holds back a vast reservoir that could cause catastrophic flooding if it burst.

The technician inside the complex said rising water levels in recent days had submerged some equipment in its lower levels.

"Because the dam has been out of service for three straight days, the technical equipment in the lower levels of the dam is under water," the technician said. "This rise in the level of the reservoir means that one of the spillways must be opened to drain the water so it does not build up, which would pose a growing threat to the dam."

The technician and the Syrian Observatory for Human Rights said the dam's main control room had been knocked out.

The technician said engineers had arrived from SDF-controlled territory and would "try to enter the dam and carry out the necessary maintenance as quickly as possible, if they are allowed".

The SDF paused fighting for four hours on Monday to allow technicians to enter the complex and carry out maintenance.