Production at Libya's El Feel oilfield was stopped on Thursday, a tribal leader and an oil engineer told Reuters by telephone.
The stoppage is considered as a protest over the kidnapping of a former finance minister, according to the tribal leader.
El Feel field, has a capacity of 70,000 barrels per day, is operated by Mellitah Oil and Gas which is a joint venture between the state oil firm NOC and Italy's Eni.
No immediate comments were available by the NOC.
The oil engineer said a number of protesters entered the field and had forced the staff to leave after operations were shut down.
"The field [El Feel] has stopped," the engineer said.
The leader of Zawi tribe, Al-Senussi al-Ahlaiq, told Reuters by telephone that the closure of El Feel aims to pressure the authorities in Tripoli to release their son Faraj Bumatari the finance minister in the former government in a protest for his "kidnapping after he arrived at Mitiga airport" on Tuesday.
The tribe threatened in a recorded statement on Wednesday evening that they will shut down oil facilities until their son Bumatari is freed.
"The matter will be greater and preperations are going on too to close the water supply to Tripoli," Al-Ahlaiq said.
Bumatari is a candidate to position of central bank governor, the tribe said in a written statement, adding that "makes him vulnerable to danger and kidnapping."
Libyan oil output has been subjected to repeated closures for different political reasons and local protesters' demands during the chaotic decade since the 2011 NATO-backed uprising against Muammar Gaddafi.
(Reuters)