Libya's National Oil Corporation (NOC) has expressed "concern" over an increased military presence at the Ras Lanuf oil terminal.
It fears the export facility is "a military objective."
"These actions could result in the withdrawal of NOC personnel from the port for their safety," the oil company said.
A group of around 80 military personnel under the command of Major General Abdullah Nur al-Din al-Hamali entered the port last Wednesday, it added.
NOC claimed the group has taken over a building within the terminal and is converting it for military use.
In addition, forces have attempted to fuel a warship, appropriated meals designated for staff, and seized 31 dormitories allocated to employees of Harouge Oil Operations (HOO), the NOC subsidiary operating the port.
“NOC works on behalf of all Libyans,” said NOC chairman Mustafa Sanalla. “We cannot accept a situation where any party to the current conflict misuses oil facilities.
“The presence of forces inside the terminal represents an unacceptable risk to employees. This renders the terminal a potential military target, thereby risking the destruction of Libyan oil infrastructure - and the resulting economic crisis that would follow.”