Libyan National Army on Thursday said they had released a Turkish-owned ship, after seizing it over the weekend in Libyan waters.
Haftar's high command "released the Mabrooka, flying a Jamaican flag, after inspecting it and completing its investigation with the crew", said Ahmed al-Mesmari, the spokesman for his forces.
The boat and crew were allowed to proceed "after paying a fine" for entering Libyan waters without authorisation and travelling in a "forbidden zone".
Haftar's forces oppose Libya's Turkish-backed Government of National Accord (GNA). Haftar is supported by the United Arab Emirates, Egypt and Russia.
His troops launched an offensive on the capital Tripoli, the seat of the GNA, in April 2019, but were beaten back in June this year, before the two sides formally agreed a ceasefire in October.
"We recall yet again that Turkish interests in Libya are targeted. There will be serious consequences and the perpetrators will be considered legitimate targets," the ministry said on Tuesday.
Mesmari had announced on Monday that the commercial vessel had entered into a "zone of military operations" in the Ras al-Hilal region and was therefore seized on Sunday and towed to port.
The crew consists of nine Turks, seven Indians and one Azerbaijani.
Libya has been wracked by violence and chaos since the toppling and killing of dictator Moamer Kadhafi in 2011.
*This story was edited by Ahram Online.