Gunmen have cut off the main water pipeline to Libya's besieged capital, Tripoli, spelling more misery for residents already reeling from weeks of fighting.

The United Nations said the water blockage was a possible war crime as Libya's internationally recognized government accused forces loyal to Khalifa Hifter, which have been trying to capture Tripoli, of being behind the blockage.

The group on Sunday raided a station of the Great Man-Made River Project, a pipe network supplying ground water from the Sahara, the company said. The gunmen forced employees to turn off the pipes at the installation 400 km (250 miles) south of Tripoli.