Government forces killed six civilians in the city of Misrata today in an unrelenting campaign of shelling and sniper fire aimed at driving rebels from the main city they hold in western Libya, medical officials said.

Doctors said 243 people have been killed and some 1,000 injured in more than a month and a half of fighting between Muammar Gaddafi's forces and rebels in Misrata. Most of those killed today were hit by snipers, they said.

One said government forces appeared to be trying to wound civilians.

"The weapons that the Gaddafi brigades use are not meant to prevent movement in the city, but to cause also deformation or paralysis so the suffering of the people endures all their lives," the doctor said.

Meanwhile, Nato said it was investigating reports that a coalition warplane had struck a rebel position which was firing into the air near the eastern front line of the battle with Colonel Gaddafi's forces.

Rebels said a group of opposition fighters was hit by an air strike about 12 miles (20km) east of Brega last night.

Mohammad Bedrise, a doctor in a nearby hospital, said three burned bodies had been brought in by men who said they had been hit after firing a heavy machine gun in the air in celebration.

Idris Kadiki, a 38-year-old mechanical engineer, said he had seen an ambulance and three cars burning after an air strike.

Nato spokeswoman Oana Lungescu said the coalition was looking into the reports.

The loosely organised rebel force had been acting in a more disciplined fashion in recent days. Yesterday only former military officers and the lightly trained volunteers serving under them were allowed on the front lines. Some were recent arrivals, hoping to rally against forces loyal to the Libyan leader who have pushed rebels back about 100 miles (160km) this week.

The better organised fighters, unlike some of their predecessors, can tell the difference between incoming and outgoing fire. They know how to avoid sticking to the roads, a weakness in the untrained forces that Col Gaddafi's troops have exploited. And they know how to take orders.

The greater organisation was a sign that military forces which split from the regime to join the rebellion were finally taking a greater role in the fight after weeks trying to organise. Fighters cheered yesterday as one of their top commanders - former Interior Minister Abdel-Fattah Younis - drove by in a convoy towards the front.

It was too early to say if the improvements will tip the fight in the rebels' favour. They have been struggling to exploit the opportunity opened by international airstrikes hammering Col Gaddafi's forces since March 19.

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