Paris - The UN's special envoy on Libya on Tuesday called on all the country's armed groups to unite against ISIS. "The fight against Daesh, which is the number one enemy, must be a Libyan fight and a united fight," said Martin Kobler, using an Arabic acronym for ISIS, after meeting French Foreign Minister Jean-Marc Ayrault in Paris.He said the rival administrations that have established themselves since the fall of long-time dictator Muammar Gaddhafi in 2011 should "unite their efforts" into a single army."A national Libyan army must be put in place," agreed Ayrault, while accepting that this was still "a long way off". ISIS have built a stronghold in Sirte, a city 400km east of Tripoli.Kobler and Ayrault reaffirmed their support for the UN-backed unity government set up in the capital two months ago. The unity government has military assets and the backing of key economic institutions, but is vehemently opposed by a rival administration in the east, which controls several militias and parts of the national army loyal to controversial General Khalifa Haftar.