* Armed brigade forced Sharara shut down late on Sunday
* Production resumes on Wed, force majeure lifted
* Giant oilfield frequently disrupted by security issues (Updates with NOC statement, force majeure lifted, details)
By Ahmed Elumami and Ahmad Ghaddar
TRIPOLI/LONDON, Oct 4 (Reuters) - Production at Libya's giant Sharara oilfield resumed on Wednesday after an armed brigade forced a two-day shutdown, the National Oil Corporation (NOC) said.
Operations at Sharara, which is crucial to a partial revival of Libya's oil output, have been repeatedly disrupted this year due to blockades by armed groups, protests and security problems.
As production resumed, the NOC lifted force majeure on loadings of Sharara crude from Zawiya port, where the tanker Seaways Hatteras was due to load a 130,000 tonne cargo, according to shipping fixtures and a Libyan oil source.
Sharara, which the NOC operates in partnership with oil companies Repsol, Total, OMV and Statoil, was shut on Sunday night by an armed group called Brigade 30, which issued a series of demands. They included requests for salary payments, fuel supplies and the release of members of the group that it said had been detained.
The field, which had been pumping more than 230,000 barrels per day (bpd) immediately before the shutdown, restarted at around 8 a.m. local time (0700 GMT) on Wednesday, NOC Chairman Mustafa Sanalla told Reuters.
The NOC did not say how the dispute had been resolved, but it thanked the head of the guard force tasked with protecting Sharara as well as senior figures from the Tuareg ethnic group for helping to restart the field.
The restart of production at Sharara added to pressure on oil prices on Wednesday, which slipped amid concerns that a recent rally had been overdone.
The NOC said losses from the closure were estimated at more than $27 million.
An engineer at the field confirmed that production had resumed.
The field has been producing up to 280,000 bpd in recent months. The North African state had been pumping around one million bpd before the latest shutdown, Sanalla said, about four times more than in mid-2016.
Libya's production has fluctuated sharply due to action by armed groups, political disputes and damage to oil infrastructure. Before the country's 2011 uprising, it stood at about 1.6 million bpd.
The recent rise in Libyan production has complicated an OPEC-led push to cut global production and bolster oil prices, from which Libya is exempt. (Additional reporting by Aidan Lewis in Tunis and Ayman al-Warfalli in Benghazi, writing by Aidan Lewis; Editing by Jason Neely and Susan Fenton)