Armed federalists have forced two oil terminals to shut down in eastern Libya in protest over not being granted more seats in this weekend's first elections since Moamer Kadhafi was overthrown.
The move on Thursday to shut down pumping and loading at the port in Ras Lanuf came as people seeking autonomy in Libya's oil-rich east threatened to boycott or even sabotage Saturday's election for a General National Congress.
Ibrahim al-Jadhran, a protest leader, said demonstrators had also blocked the port of Al-Sidra, 35 kilometres (20 miles) west of Ras Lanuf, and were heading eastward to the oil terminal of Brega.
Earlier, on Thursday, suspected arson ravaged a depot containing electoral material in the eastern city of Ajdabiya, destroying ballot papers, lists of candidates, political parties and voters, and other items.
And on Sunday, armed men ransacked election offices in the eastern city of Benghazi, cradle of the revolution that ousted Kadhafi last year and a bastion of the federalist movement that wants greater autonomy from Tripoli.
The weeks before the election have been marred by fighting between different communities, with bloody clashes in western hilltop towns claiming more than 100 lives and fighting in Kufra in the south leaving dozens dead.
"The harbour is closed... The pumping and loading of oil has been stopped... The group that came were federalists," Tumi Shakari, a supervisor at a major oil terminal in Ras Lanuf, said on Thursday.
"A group of 15 people came around 9:30 pm (1930 GMT) and in a very peaceful and amicable manner asked us to shut down operations," the supervisor added.
"This group has certain demands that they want to see fulfilled and they have asked us to stop our work for 48 hours," he continued, adding that workers had complied to avoid an escalation.
On Friday morning, Milad Mohamed Ali, superintendent of the Al-Haruj terminal, just west of Ras Lanuf, said "the situation remains the same since last night."
"The government must do something about this. This is their way of seeking attention for their demands," he added
Tareq al-Tahi, senior superintendent at Al-Sidra, confirmed the terminal had been shut.
"We have been forced to stop production," he told an AFP reporter on site.
"At 7:30 pm (1730 GMT) a group of people came to us in armoured vehicles loaded with anti-aircraft guns and asked us to stop producing oil and loading cargo," Tahi added.
"The situation is the same in Ras Lanuf, Brega, and Haruj (near Ras Lanuf)."
The demands of federalists in the east are not the only concern to the government and international community ahead of the election.
Security services have wared that supporters of the former regime may seize the opportunity to disrupt the vote to elect a national assembly, which will be tasked with appointing a new government.
And Islamist groups in the east also oppose the vote, saying the devoutly Muslim country needs no constitution other than the Koran.
The outgoing National Transitional Council said on Thursday that Islamic law (sharia) should be the "main" source of legislation and that this should not be subject to a referendum.
One of the central demands of the federalist movement is an equal allocation of seats in the 200-member assembly.
The interim authorities, on the basis of demographic considerations, gave 100 seats to the west, 60 to the east and 40 to the south.
The new assembly was to have become an interim legislature, appoint a new government and a panel to draft a new constitution.
But on Thursday, the NTC abruptly changed the rules it had itself set, saying the constituent authority must be elected separately rather than appointed.
That decision strips the General National Congress of what was to have been one of its core functions, but it will retain its legislative powers and the prerogative of appointing a government.
The amendment came in "response to demands made by a significant part of the population," according to NTC spokesman Saleh Darhoub.
An NTC delegate was more direct, saying its primary purpose was to appease the federalist faction.
Oil production is the major source of government revenues in Libya, and has reached 1.55 million barrels per day, nearing pre-war levels, officials say.
Production of several oil companies goes through Ras Lanuf, including Libya's AGOCO (55,000 barrels per day), Germany's Wintershall (70,000 bpd) and Al-Haruj (80,000 bpd), according to industry experts.
The oil complex at Ras Lanuf lies 360 kilometres (225 miles) west of the eastern city of Benghazi, birthplace of the revolt that ousted Kadhafi, who was captured and killed in October.
A former rebel manning a checkpoint on the coastal highway said: "We closed the terminal because we want our demands to be fulfilled. This is an issue of seat allocations."