NATO warplanes mistakenly destroyed a tank captured from Libyan leader Moamer Kadhafi's forces in the western port town of Zawiyah, killing four rebels, an AFP photographer said on Sunday.
The tank was captured on Saturday when the rebels launched an assault on the town, overrunning the western sector but encountering fierce resistance from Kadhafi's troops who took up positions in the east, the photographer said.
Rebels on the ground said they were driving the tank out of Zawiyah when the NATO warplanes struck, destroying the vehicle.
The photographer saw pools of blood in front of the tank and was told four insurgents had been killed in the air strike.
NATO said in its daily update that its warplanes struck two tanks in Zawiyah on Saturday, out of 13 hits around the country.
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UN Security Council Resolution 1973 authorised NATO in March to defend Libya's civilian population from attacks by Kadhafi's regime, which faces a popular revolt after 42 years in power.
Under the mandate, NATO planes regularly attack Kadhafi's military assets, including tanks, armoured vehicles, rocket launchers, army bases and munitions dumps.
Late Saturday, the Libyan government insisted Zawiyah remained under regime control after the rebels told an Arabic satellite channel they had completely overrun the city.
Government spokesman Mussa Ibrahim told reporters in Tripoli that less than 100 fighters tried to enter the town to join up with about 50 rebels inside Zawiyah.
"This is not an advance. This is what you call a skirmish, what you call a suicide mission," he said. "You have to remember we are very powerful. Tens of thousands of volunteers are armed right now."
In a spurt of military activity, rebels fighting east of Tripoli said they strengthened their grip on the town of Tuarga in a bid to create a buffer zone between Kadhafi's forces and the city of Misrata.
The rebels have launched numerous unsuccessful assaults on the port, some 50 kilometres (32 miles) west of Tripoli, that they they lost to Kadhafi's forces in March.