Exports from the smaller El Feel oilfield were continuing, field engineers said, as workers had maintained its power supply, which is shared with El Sharara. El Sharara closed last week after tribesmen and security guards took it over.

Production from El Sharara, located in the south of the North African OPEC member country, will restart only after "alternative security arrangements are put in place", NOC said in a statement late on Monday.

"Clearly we cannot return to the security situation we were in before the field was shut," NOC Chairman Mustafa Sanalla was quoted as saying in the statement.

The local militia group that seized the 315,000-barrels-per-day (bpd) El Sharara is demanding payments and development funds for the neglected south, NOC said.

El Feel, also located in the south, has not been affected and is pumping around 70,000 bpd, a field engineer said.

Its exports were being routed via the Melittah oil and gas port, which like El Feel belongs to a joint venture NOC has with Italian energy company Eni, another engineer said.

A spokesman for NOC could not be reached for comment.

El Sharara crude is normally routed to the Zawiya port, home also to a refinery. NOC runs the field with Spain's Repsol , France's Total, Austria's OMV and Norway's Equinor, formerly known as Statoil.