A bomb exploded at an oil pipeline from Libya's El Sarir field on Saturday, halting flows to Hariga port as the country struggles to restore crude exports battered by factional fighting.
In a separate incident, gunmen stormed government buildings in the coastal city of Sirte, forcing officials out at gunpoint and taking over administrative offices and television and radio stations, the state news agency said.
No more details were immediately available. Several Islamist militant groups are active in Sirte.
Libya is riven by conflict, with two rival governments operating their own armed forces and separate parliaments, nearly four years after the civil war that led to the overthrow and killing of leader Muammar Qaddafi.
The fighting also involves Islamist militant groups, former rebels, ex-Qaddafi troops and tribal and federalist factions often pursuing local causes.
No group claimed responsibility for Saturday's pipeline bombing. Oil infrastructure, ports and pipelines in the North African OPEC member state are often targets of attack.
Hariga oil terminal supervisor Rajab Abdulrasoul told Reuters on Saturday the bomb went off at around 5 a.m.
"A bomb exploded at a pipeline carrying crude between El Sarir oil field and Hariga port," he said. "The firefighters are still trying to put out the fire. What happened is sabotage."
A spokesman for the National Oil Corporation said a tanker had been loading up with crude at Hariga. He said it could take up to three days to restore the pipeline.
Hariga had just reopened after a strike by guards there. The country's two main oil ports and nearby fields are still closed after clashes between rival armed groups trying to gain control of them.
Libya's oil production has fallen to around 350,000 barrels a day, a fraction of the 1.6 million bpd Libya used to pump before the NATO-backed 2011 uprising that ended Gaddafi's rule.
Two gunmen attacked Tripoli's Corinthia hotel last month, killing nine people, including five foreigners, in an attack claimed by militants who said they were loyal to Islamic State.
Earlier this month, south of Sirte, gunmen killed 12 people, among them two Filipino and two Ghanaian nationals, after storming a remote oilfield. Officials said most of the victims were beheaded or shot.
French and Libyan officials said Islamic State of Iraq and Syria (ISIS) militants were behind the attack on the oilfield, in which France's Total has a stake, but which is operated by a Libyan company.SHOW MORE