Crude oil shipments from Libya, the world's 12th largest exporter, have almost halted as reduced production, a lack of staff at ports and security concerns due to violence take their toll, industry sources said on Friday.

A violent uprising against leader Muammar Gaddafi's 41-year rule has deterred some shippers from sailing to Libya, with some vessels refusing to dock at Libyan ports or turning back.

You can't get into those ports. There is zero communication, said a buyer of Libyan crude. We've heard reports of vessels turning around.

Bad weather in the Mediterranean has also disrupted operations, the sources said.

Shipping sources said at least five tankers with around 3 million barrels of crude oil were being held up by disruptions.

The turmoil in Libya and the prospect of the loss of its 1.3 million barrels per day (bpd) of crude oil exports have sent oil prices soaring. Brent crude rose to almost $120 a barrel on Thursday, the highest since 2008.

Port lists shown to Reuters by traders buying Libyan crude said the eastern ports of Marsa el Hariga and Zuetina linked to one of the country's largest oilfields Sarir were closed.

They also showed that the key Zawiyah port in western Libya, fed by the Murzuk oilfields, was shut due to stormy weather.

Industry sources said on Friday the Es Sider terminal was believed to be in operation.

It is a combination of disruptions and bad weather, said another oil trader with an oil company that buys Libyan oil.

The Libyan coastal town of Zawiyah was under the control of anti-government protesters on Friday, a witness said, bringing the popular uprising against Gaddafi within 50 km of the capital Tripoli.

Five of the country's six major oil export terminals are located in eastern Libya, according to the International Energy Agency, an area partly controlled by rebels.

At least 60 percent or 958,000 barrels per day of January crude exports left from eastern ports, according to the International Energy Agency.

The captain of the tanker we chartered refused to go to Libya, said a source with a major oil company. He said he was concerned about the security of the port.

An official with Greek group Polembros Shipping Ltd said one of its tankers was loaded at Es Sider with another still waiting to enter the port due to the bad weather.

Both vessels, bound for Europe, were aframaxes, a tanker which usually carries up to 600,000 barrels on Med routes.

PORT STAFF

A separate Greek shipping source said one of their aframaxes was at anchorage outside Zawiyah port, while a second tanker was waiting in a queue outside Ras Lanuf.

Libya normally produces about 1.6 million bpd of high-quality oil, or almost 2 percent of world output.

Between 30 percent and 75 percent of output has been shut down due to the turmoil in the country.

Port staff not working at Libyan ports creates difficulties for owners with vessels at quays, which need for example tugs to get their ships out to sea again, said Peter Sand, shipping analyst with ship association BIMCO.

But no ships have been involved in any of the violence so far.

A ship insurance source said they were watching to see if workers turned up for work on Saturday.

Our experience in Egypt was that the key determinant of whether ports will operate or not was whether port workers were sufficiently confident of their safety to make the trip to work, the source said.

(Additional reporting by Ikuko Kurahone and Christopher Johnson in London and Renee Maltezou in Athens; writing by Alex Lawler; editing by James Jukwey)

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