But while some fighters put some of the blame on a poorly organised advance by the advancing fighters, others suspected betrayal from some inside their own ranks.

"I did not fire one shot today because there was nothing clear to shoot at... They are shooting at us from above and we can't see anyone," said Commander Abdel Monem, 28, from Zawiyah.

Fighters backing the National Transitional Council (NTC) had made a disorganised advance into uncharted territory, he added.

Novices had been mixed in with the veterans and there had been almost no coordination between them.

"In one word: it was chaos," he said.

The oasis town, a stronghold of the powerful Warfalla tribe, is one of the last places still loyal to Qadhafi. Efforts by the NTC in recent days to negotiate a peaceful occupation foundered.

Taking Bani Walid will be no easy task, as pro-Qadhafi fighters within the town have the higher ground. Attacking fighters have to stream in through the valley, making them an easy target for an ambush.

The main challenge, said Monem, was snipers perched on the hills and residents armed by Qadhafi.

They have been led to expect the worst from the NTC force after an intense propaganda campaign that has depicted them as killers and rapists.

"Civilians are afraid of us because Libya TV said we are rats that will rape their daughters," he said. The lack of electricity in the Bani Walid area had prevented the NTC from countering that message, he added.

All afternoon, a local pro-Qadhafi radio station broadcast an appeal to residents to rally against the invaders.

"They want to spread corruption and destruction everywhere. Go today, today, today -- now you are armed there is no excuse. This is the time for jihad (holy warfare)," it said.

NTC fighters backed by armoured vehicles mounted with anti-aircraft guns arrived early Sunday on the edge of Bani Walid, 180 kilometres from Tripoli, an AFP correspondent said.

The fighters said they had routed Qadhafi loyalists and snipers from Wadi Dinar, a valley in the shadow of Bani Walid, during their Saturday advance towards the town.

By Sunday, they were sending in scouting missions to probe the defences.

Clashes erupted in the afternoon in the neighbourhoods of Al-Mansila and Al-Hawasim, according to one fighter, Ahmed al-Warfalli, and two shells crashed into a hill six kilometres (four miles) north of the town.

NATO warplanes and explosions could be heard throughout the day.

There were contradictory accounts however as to how far rebels had advanced into the city and the strength of the resistance they had encountered.

Military commanders insisted that the main assault had yet to begin.

"Today we are still on standby and waiting for orders," said one commander, General Atiya Ali Tarhuni, earlier in the day.

But by evening ambulances were rushing to and from the front line. An AFP reporter counted three fighters killed and 15 wounded. Rebel fighters said they had lost as many as 10 men.

An emergency services doctor operating a field clinic in the hamlet of Wishtata, 40 kilometres from Bani Walid, said most of the wounded had been treated for sniper shots and explosions.

"There are Qadhafi military people in the heights of Bani Walid shooting down at rebels," said Dr Mehdi Barut.

At dusk, a pick-up truck arrived with four men the fighters said were pro-Qadhafi prisoners. They were locked in a side building in the same compound of the clinic and drew crowds thirsty for revenge.

Sami Saadi Abu Rweis, a fighter returning from Bani Walid with a wounded friend in tow, reported snipers everywhere.

"They are shooting at us from two kilometres away. Bani Walid is full of arms -- every household has them.

"There is some type of treason going on. People pretended to be with the rebels but are really with Qadhafi."

Fighters released their frustration by firing their weapons into the air as rumours of betrayal spread like wildfire, raising tensions in the ranks.

Many grilled comrades who had pulled out early, while others became agitated when they discovered that one of the casualties had a bullet to his neck apparently caused by a shot that had come from behind.

"One hundred percent there was treason," said Hamza Bashir, age 22, a fighter from Tipoli close to tears.

"We need better organisation and cooperation from Bani Walid's residents," concluded Monem. He was hesitant to bring one hundred of his men based in the capital to a battle seemingly doomed to be a suicide mission, he added.

"You can bring 1,000 men but without organisation nothing will go right."