* Disruptions at some Libyan ports still continuing
* Concerns that violence could escalate further
(Adds comment, detail, background)
By Jonathan Saul and Renee Maltezou
LONDON/ATHENS, March 2 (Reuters) - At least 2.4 million barrels of crude oil in four tankers have left Libyan ports in the past 24 hours despite mounting violence in Africa's third largest producer, shipping and trade sources said on Wednesday.
Forces loyal to Muammar Gaddafi attacked the major oil export terminal of Marsa El Brega in the first sign of a counter-offensive by Libya's leader in the rebel-controlled east, which rebels said they had repulsed. [ID:nLDE72115X]
As fighting continues across Libya, the oil industry is trying to assess the output lost, with outage estimates currently around 800,000 barrels per day (bpd).
Shipping and trade sources said two cargoes were exported from the port of Zawiyah close to Tripoli with another sailing from Zueitina in the east in the past 24 hours.
A further cargo left from Marsa el Brega earlier on Wednesday despite clashes there.
"We had a tanker in Zueitina, which left yesterday," a Greek shipping source said. "We hear that most ports are open, some are under operating but are open. Some were forced to shut due to bad weather, but crude oil is leaving the country."
Shipping and trade sources said on Monday crude oil shipments were at a virtual standstill due to bad weather and other disruptions. But since then tankers have been loading crude oil and various types of oil products.
The sources said at least two tankers were waiting to pick up cargoes in Zawiyah and Mellitah. "Zawiyah is working normally and our ship left this morning," one source said.
The sources said more than 2 million barrels of crude were exported between Monday and Tuesday. [ID:nLDE7202K9]
Crude oil traders said the port of Es Sider was also operating.
But ongoing communications difficulties with phones and internet issues with Libya had led to some cargoes being cancelled this week, shipping sources said.
It was also unclear if some terminals were still receiving oil. Teekay Tankers (TNK.N) said on Tuesday one of its vessels had received only half a cargo at the major port of Ras Lanuf. <^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Factbox on Libyan oil production [ID:nLDE72018W] Libyan oil map r.reuters.com/jem28r Oil choke points: link.reuters.com/cuh38r Map of Libya towns and incidents:
r.reuters.com/fug38r here ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^>
Shokri Ghanem, chairman of Libya's National Oil Corporation, said on Wednesday the country's oil output had fallen to 700,000 to 750,000 bpd due to the worst crisis for Libya's oil industry in decades. [ID:nSGE72103A]
Anti-Gaddafi forces have been firmly in charge of eastern Libya up to Marsa El Brega and some areas beyond, since shortly after anti-government protests erupted in mid-February.
"There are more clashes on land, which makes it unsafe for people to work and I think the situation has been worse today," said a shipper who moved a cargo on Wednesday. "The flow of oil might be reduced further." (Additional reporting by Emma Farge and Alex Lawler in London; writing by Jonathan Saul; editing by James Jukwey)