|Misurata, Libya's third largest city, has been under siege since rebels drove out Gaddafi loyalists two months ago [AFP]
Libyan government forces have dropped bombs on four large oil-storage tanks in the contested western city of Misurata, destroying the facilities and sparking a fire that spread to four more, according to an opposition spokesman.
Government forces used small, pesticide-spraying planes for the overnight attack in Qasr Ahmed close to the port, Ahmed Hassan, the spokesman, said on Saturday.
Misurata is the last remaining city in the west under rebel control. It has been under siege for more than two months and has been the scene of some of the war's fiercest fighting between the rebels and loyalists of Muammar Gaddafi, Libya's long-time ruler.
Hassan said the rebels notified NATO about the aircraft before the attack but there was no response.
"Four tanks were totally destroyed and huge fire erupted which spread now to the other four. We cannot extinguish it because we do not have the right tools," he said.
"Now the city will face a major problem. Those were the only source of fuel for the city. These tanks could have kept the city for three months with enough fuel."
Gaddafi's forces flew at least one helicopter reconnaissance mission over Misurata last month, according to the rebels.
Al Jazeera's Tony Birtley, reporting on Saturday from Benghazi, the rebel stronghold in eastern Libya, said that the reported attack in Misurata was very disconcerting for the people who rely on the stored fuel.
"People are raising questions because NATO patrols the skies 24 hours a day," he said.
"This incident, together with the mines in the harbour, are very worrying for the locals."
The rebels have also accused Gaddafi of using helicopters bearing the Red Cross emblem of dropping mines into Misurata's harbour.
Suleiman Fortiya, who represents Misurata on the rebel interim National Transitional Council, said small helicopters flew over Misurata on Thursday and Friday to drop mines.
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"They had Red Crescent and Red Cross markers so that anyone who sees them thinks it is for humanitarian aid," he said.
An aid worker said he saw helicopters on Friday marked with the Red Crescent circling above the port and dropping mines into the sea.
NATO confirmed that helicopters had flown over Misurata on Thursday in breach of the no-fly zone that its jets are supposed to enforce. However, it could not confirm that the helicopters were marked with the Red Cross sign.
NATO official told the AFP news agency a ship involved in the the coalition's operations had observed a number of helicopters over Misurata on Thursday, which came under fire from rebel forces.
"We are aware of reports that the helicopters were marked with the Red Cross," the official said.
He said no humanitarian flights had been notified for the Misurata area on that day.
"Any use of the Red Cross to disguise combat forces would be a breach of international law," he said.
In another development, Al Jazeera's correspondent in Tunisia said, shells fired by Gaddafi's forces landed inside Tunisian territory near the town of Dhaiba, on the border with Libya.
The town has been hit repeatedly by stray shells in recent weeks, and on Saturday Tunisia condemned the "extremely dangerous" shelling, saying that it would take all necessary measures to protect its sovereignty.
The Libyan government denied it targeted Tunisian soil deliberately.
"We said this [shelling] was an error and we have apologised that this took place and have asked the military forces to ensure this doesn't happen again," Al-Baghdadi Ali al-Mahmoudi, the Libyan prime minister, said in Tripoli.
Fighting has intensified in Libya's western mountains region amid a stalemate in the other battle fronts.
| Hundreds of migrants have arrived on the Italian island of Lampedusa in recent weeks, fleeing the unrest in Libya
Elsewhere in the country, government forces surrounding rebel-held Zintan fired 300 rockets into the town on Saturday, Abdulrahman al-Zintani, a rebel spokesman, said.
He gave no details of casualties in Zintan, which is largely empty of civilians.
"NATO aircraft can be heard but there have been no air strikes," al-Zintani told Reuters.
Also on Saturday, a migrant boat laden with 600 men, women and children - mostly African refugees - sunk off the coast of Tripoli.
Al Jazeera's Karl Stagno-Navarra, reporting from the nearby island of Malta, said that most of those on the boat were feared dead. He said that a rescue operation was under way and a few bodies had been recovered.
"The information we are receiving from the island of Malta, with regards to this boat, is that so far only 15 have managed to reach the shores after they swam for about two hours," he said.
"Meanwhile, we understand that this was one of two boats that left Tripoli on Friday which was headed for Italy.
"Tonight we learn that a number of those migrants who reached Lampedusa in the first boat are now claiming to have received phone calls from relatives both in Libya and on mainland Italy to inform them that their relatives on board the second boat, which went down, are now dead."