Libyan oil port activity was tailing off on Thursday, but despite civil unrest tankers were still leaving and waiting to enter the country's ports, sources said on Thursday.

At least one empty tanker left a Libyan terminal on Thursday to take on cargo in Egypt, and at least two more tankers were waiting to enter Libyan ports.

The one million barrel capacity tanker Sanandaj, owned by the National Iranian Tanker Company (NIT), left the port of Benghazi empty on Thursday morning destined for Egypt's Sidi Kerir petroleum terminal in Alexandria to pick up cargo, a company spokesman said.

Another million barrel capacity tanker owned by NIT, the Sarv, was anchored outside the port of Tobruk on Thursday, waiting to enter Libyan oil company Agoco's Marsa El Hariga petroleum terminal, according to AIS Live ship tracking data on Reuters. It was not clear whether it was to take on cargo or offload.

A slightly smaller tanker was waiting to enter Libya's port of Mellitah in order to take on cargo, a shipping source said.

"The situation is very unclear; ports are theoretically open, but in practice they are almost closed because we are giving priority to passenger ships," a spokesman for the Libya Shipping & Maritime Agency in Tripoli said.

Despite this, at least 2.4 million barrels of crude oil in four tankers left Libyan ports earlier this week, shipping and trade sources said.

Forces loyal to Libyan leader Muammar Gaddafi attacked the major oil export terminal of Marsa El Brega on Wednesday in the first sign of a counter-offensive by the leader in the rebel-controlled east, which rebels said they had repulsed.

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).

Ongoing communications difficulties with phones and the internet in Libya led to some cargoes being cancelled this week, shipping sources said.

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.