Troops loyal to Muammar Gaddafi on Sunday pounded the western town of Misurata, which has been under its siege for weeks, as rebel forces in the east were involved in a seesaw desert battle for control of the strategic oil town of Brega.
Massive shelling by government forces killed at least one person and wounded several others in Misurata, the country's third largest city and the main rebel stronghold in the west.
It is unclear who controls Brega, which has been the scene of fierce fighting over the past few days when pro-Gaddafi forces returned after being driven out by rebel forces.
Amid conflicting reports, the rebels claimed that they had regained control over Brega, 800 km east of Tripoli, that has seen a see-saw battle after Gaddafi's forces struck hard at the rebels who had earlier pushed them out.
However, the opposition's advance appeared to be slow and uncertain despite two weeks of air strikes targeting the Gaddafi regime by the western military coalition, Al Jazeera channel said.
The Arab channel said the opposition forces have advanced to a walled university campus near the town's western edge. "If you compare where we are today to where we were a few weeks ago, then we are in the exact same position," it said.
According to BBC, a doctor in Misurata, 214 kilometres east of the capital Tripoli, said his clinic was overwhelmed.
"We have one killed, three in the operating room now, one with an amputated leg, we have one in ICU (intensive care) because of shell fragments in his chest and we have six wounded with different wounds and they are waiting for an operation but we have only three operating rooms," Al Jazeera quoted Ayman as telling BBC.
At least 13 rebels were killed in a "regrettable" NATO airstrike near Brega yesterday. NATO said it was ascertaining reports that a coalition warplane hit a rebel position in the midst of heavy fighting with Gaddafi's forces.
Al Jazeera and BBC reports said a rebel convoy on its way to the front line near Brega fired an anti-aircraft gun into the air. Assuming it to have come from Gaddafi's forces, coalition warplane targeted the vehicles.
"We are looking into these reports. We are always concerned by reports of civilian casualties. NATO's mission is to protect civilians and civilian areas from the threat of attack," Oana Lungescu, a spokeswoman for NATO, was quoted as saying.
Mustafa Gheriani, a spokesperson for the opposition's Transitional National Council, said: "We understand that collateral damage may also take place and we do accept it, because we look at the big picture which saving more lives."
"The leadership is working on preventing a re-occurrence."