By Feras Bosalum and Julia Payne
TRIPOLI/LONDON (Reuters) - Striking security guards reimposed a two-week-old shutdown at Libya's two biggest crude export terminals on Monday, hours after they had reopened, and more oilfields closed in a wave of protest that is propping up world oil prices.
The outages at ports and fields, caused by striking employees and jobless people demanding work, have brought the worst disruption to the North African OPEC member's oil industry since the civil war in 2011.
A source at Arabian Gulf Oil Company (AGOCO) said output at the state oil company subsidiary had dropped below 60,000 barrels per day (bpd) due to strikes, down from levels of 375,000 bpd before the disruption.
Meanwhile, loadings halted again at the Es Sider and Ras Lanuf terminals, with a combined export capacity of 600,000 bpd, due to actions by the armed guards whose job is to protect them, trading and shipping sources said.
"The security guards have stopped the exports (from Es Sider)," said Mohammed El-Hattab, chairman of the federation of oil workers and an employee at the port's operator Waha Oil Company.
"We are having discussions now and hope to restart today or tomorrow," he added.
In total, around 15 crude and oil product tankers were waiting outside the two ports, according to Windward, a maritime analytics services company.
The blows to exports from Libya, OPEC's ninth largest producer, as well as the prospect of lower Iraqi shipments have limited falls in benchmark Brent crude oil futures, traders said. Brent was 39 cents lower at $107.83 a barrel by 9:38 a.m. ET.
European refineries are having to pay high prices for alternatives due to a shortage of light sweet Libyan crude oil as exports were below 500,000 bpd at the end of last week, less than half of its recent rate of about 1 million bpd.
One industry source with close ties in Libya estimated Monday's output at around 540,000 bpd, adding that the Brega and offshore Al Jurf and Bouri fields were among those operating.
Several trading sources reported, however, that the 130,000 bpd El Feel field, shut since end-May, has started to ramp up production - a sign of the fast-evolving situation in the labor and social protests sweeping across Libya's economy.
But AGOCO's latest outages add to those at the Es Sider, Amna and Sirtica producing fields, which were closed early last week due to storage limits.
AGOCO's Sarir, Nafoora and two small oilfields were shut while the Mesla field and Hamada fields were producing around 50,000 bpd and 10,000 bpd, so far.
"If the situation continues...we could be forced to halt production completely at Mesla field when we reach maximum storage capacity," an AGOCO company document showed.
At the coast, the port Marsa al Hariga, which handles the Sarir export grade of crude and feeds the oil refinery at Ras Lanuf, has also been closed, a company source said.
Trading sources said the port of Zueitina was still closed and that the Zawia port in the west and the major El Sharara field were still operating.
Operators of shut terminals had hoped that negotiations would lead to their reopening after the Eid al-Fitr holiday marking the end of the Muslim fasting month of Ramadan, and the stoppage was lifted on Sunday at Es Sider.
But the resumption was short-lived at the terminal operated by Waha, a joint venture between Marathon, Hess and ConocoPhillips with Libya's state National Oil Corporation (NOC).
The Ras Lanuf terminal is operated by Harouge Oil Operations, a joint venture between Canada's Suncor and Libya's state National Oil Corporation (NOC).
(Additional reporting by Ron Bousso and Lin Noueihed in London; Editing by Anthony Barker)