Libyan tribesmen protested at the giant El Sharara oilfield on Saturday and shut down production, the force guarding the facility and a spokesman for the protesters said.
State oil firm NOC had no immediate comment. Closing down an oilfield takes time. Engineers at the field had earlier given conflicting reports about whether oil was flowing or was being halted.
The tribesmen calling themselves the Fezzan Anger Movement were protesting to demand more development help for their community. Fezzan is the historic name of the southern region of Libya where El Sharara oilfield is located.
"El Sharara is closed. We had given authorities a deadline but we got no response," said the group's spokesman Mohammad Maighal.
The field, which usually pumps about 300,000 barrels per day, has been repeatedly threatened by tribesmen asking for better health and other state services for poor, desert region.
The state oil firm NOC usually tries to avert such action through talks.
Protesters stop output at Libya’s El Sharara oilfield