Soldiers and police have clashed in the last few days near Libya's biggest El Sharara oilfield in the south, while separate fighting erupted in the west not far from the Zawiya refinery, residents and medics said.
The violence came as video emerged on social media purportedly showing a rival oil minister appointed by an armed opposition group controlling the capital Tripoli giving a speech at the oil ministry.
If confirmed this could mean the central government has lost control of the oil ministry, potentially paralysing vital oil exports over questions of ownership.
Apparently speaking from the office of the deputy oil minister, Mashallah al-Zawie called on all Libyans for unity and to reject "conspiracies", according to the video which could not be independently verified. A spokesman for state-owned National Oil Corp (NOC), located in the same building as the ministry, declined to comment.
Libya has plunged into anarchy three years after the removal of Muammar Gaddafi. An armed group from the western city of Misrata seized Tripoli in August, forcing the elected parliament and senior officials to move to the far east.
The Misrata-group has set up its own parliament and government, which are not recognised by the international community backing the largely powerless prime minister, Abdullah al-Thinni.
In southern Libya, up to 12 people have been killed in the fighting, which broke out on Wednesday and is symptomatic of the anarchy in Libya, where the government is unable to control former rebel militias who helped Gaddafi but now fight each for control and a share of oil revenues.
The fighting started in Ubari, a half-hour drive from the El Sharara oilfield, which was shut last week because of damage to a storage facility at the Zawiya refinery in the north which it feeds.
Residents said gunmen had attacked a police station in the town, not far from the main southern city of Sabha, after a failed attempt to smuggle fellow tribesmen from the nearby border with Algeria. Around 27 people were wounded, hospital medics said.
Fighting in the west
Some commentators on Libyan social media websites linked the fighting to attempts by the Misrata alliance controlling Tripoli to get access to El Sharara.
Libyan media have reported that envoys from Misrata-based groups have visited several areas in western and southern Libya in the past few weeks to sound out the possibility of ooperation with local groups and tribes.
Misrata, Libya's third city, is home to some of the most experienced rebel militias, as well as Libya's biggest non-oil port.
But the city lacks access to oil, the only source of revenue for Libya's $47 billion annual budget. Rival militias from Zintan, who have been expelled from Tripoli by Misrata's forces, control pipelines coming from the two southern oilfields of El Sharara and El Feel.
Members of the Tibu minority, which has complained of neglect, have blocked the El Sharara field in the past to demand financial assistance or guarantees of citizenship for Tibu who come from neighbouring Algeria or Niger.
El Sharara is jointly operated by Libya's state-run National Oil Corp (NOC) and Spain's Repsol. The El Feel field, which has also been blocked on occasion by other protesters, is operated by NOC and Italy's ENI.
The El Sharara field was pumping around 200,000 barrels of oil per day until the shutdown last week. On Sunday, Ibrahim al-Awami, head of the inspection and measurement department at the Oil Ministry, said Zawiya and El Sharara remained shut, and Libya's output was down to 700,000 bpd.
Fighting was also reported in the Warshefana tribal area west of Tripoli which the Misrata forces have been trying to take for weeks. "The whole area including residential buildings has been heavily shelled," said a Warshefana official. "There are casualties," he said without giving a number.
The United Nations said it was proposing a meeting of the parties to the conflict on Sept. 29 without giving the venue, making a new attempt at talks after previous initiatives failed.
"There is a general consensus that the only solution to the current crisis in Libya is through the convening of a political dialogue that leads to an agreement on the institutional framework for...the continuation of the democratic transition process," the U.N. said in a statement.