Fears of escalation after militias enter Libya's Tripoli
The Libyan capital has been controlled by dozens of militias with shifting loyalties and territories since the overthrow of Muammar Gaddafi in 2011.
On Thursday, Mahmud Zagal, a militia commander from Misrata, announced the creation of the "Libyan National Guard", saying it would stay out of "political, party and tribal disputes".
It aims to continue the fight against the Islamic State group, secure state institutions and diplomatic missions, he said in a statement.
It did not say whether or not it would support Libya's UN-backed Government of National Accord, which has struggled to assert its authority across Libya or even control the capital.
A GNA source said on Saturday that most of the groups involved had taken part in a seven-month battle to oust IS from its stronghold of Sirte, which fell in December.
Misrata's well-armed militias, which control much of western Libya, led the fight but say the GNA stopped supporting them after Sirte fell.
Misrata's powerful militias, which led the fight, control much of western Libya.
GNA officials met on Saturday with the group's leaders "to attempt to find a solution", the source said.
Several locals said the militias included backers of Khalifa Ghweil, the leader of a self-proclaimed "Government of National Salvation" which in January tried and failed to seize three government ministries in the Libyan capital.