TRIPOLI (Reuters) - Libyan authorities are attempting to negotiate with a group that has cut water supplies to the Libyan capital for the second time in two months to press for the release of a jailed ally, an official said on Tuesday. The group shut down pipes pumping water to Tripoli and other coastal towns at the al-Hasawna well system south of the capital, said Tawfiq Shwehaidi, a manager at the Great Man Made River in the eastern city of Benghazi.  Today is the fifth day in a row that the water has stopped and we are trying to negotiate with them,  he said.  The group, loyal to late former leader Muammar Gaddafi, is demanding the release of Mabrouk Ehnaish, a militia leader detained last month by Tripoli s Special Deterrence Force (SDF), which is aligned with Libya s U.N.-backed government. Ehnaish s backers have made various threats to sabotage infrastructure including oil and gas supplies, and in October blocked water supplies to the capital for about two weeks.  The Great Man Made River is a pipeline system built under Gaddafi that pumps water to coastal areas from underneath the country s southern desert. The water cuts come as Libyans struggle to cope with a steep decline in living standards during the conflict that developed after Gaddafi s 2011 overthrow, and an economic crisis that has led to rapid inflation and severe cash shortages. In recent days there have also been long queues for fuel and cooking gas in Tripoli. Though distributors have denied any shortages, some residents nervous about disruption to supplies have queued for more than an hour to fill vehicles or jerry cans. 