Gunmen have fired at a helicopter carrying voting material for Saturday's election, killing one person, officials have said.
The helicopter made a forced landing outside the eastern town of Benghazi.
The identity of the attackers is not known, but eastern Libya has been a focus of unrest by groups seeking greater regional autonomy.
The parliamentary poll is the first national vote since Col Muammar Gaddafi was toppled last year.
The news came as armed men closed at least three oil export terminals in the east in protest at the vote.
They are angry that the west of the country has been granted more seats in the new 200-member General National Congress than the oil-rich east.
The current system allocates 100 seats to the west, 60 to the east and 40 to the south.
According to Reuters news agency, about half of Libya's oil exporting capacity has been shut down as a result.
"A helicopter carrying ballots and flying over the region of Hawari [south of Benghazi] was struck by small arms fire," AFP news agency quotes Col Ali al-Sheikhi as saying.
He said one person aboard was killed when the helicopter was struck by anti-aircraft fire.
The more than four-decade rule of Col Gaddafi, who died in October after the eight-month uprising, has left the country deeply divided along ethnic, regional and ideological lines.
The BBC's Rana Jawad in the capital, Tripoli, says the country is still awash with weapons and there are lone regional and city brigades as well as some rogue militia groups that only take orders from themselves.
More than 2,000 candidates are standing for election to the legislative body which will replace the National Transitional Council (NTC) that led the campaign against Gaddafi.
The elections have already been delayed once and in some parts of eastern Libya there are calls for a boycott.
On Thursday, a fire destroyed election materials at a depot in the eastern city of Ajdabiya, south of Benghazi, where electoral commission offices were ransacked earlier in the week.
In an attempt to defuse the tensions, the NTC has said the new parliament will now not be responsible for naming the panel that will draft Libya's new constitution.
The 60-member committee will be elected in a separate vote at a later date.