The rockets and mortars rained down on the position where the revolutionaries had retreated on the outskirts of the mountainous stronghold of Moammar Gadhafi's loyalists. So, in a fury, the fighters charged wild and unorganized Sunday back into the city for yet another day of fighting.

Fighters for Libya's new rulers have been throwing themselves into the battle to take Bani Walid for days with no progress against the old regime loyalists, strongly fortified and bristling with heavy weaponry. The frustration is showing among the amateur revolutionary fighters.

"We expected this kind of resistance from Gadhafi forces, but I thought we could take them on," said Mohannad Bendalla, a doctor treating wounded fighters at a field hospital set up outside of the city.

The official, trained military of the National Transitional Council, Libya's interim government, has pulled away from Bani Walid to regroup and reinforce for a new assault after they were heavily beaten in the city Friday. That has left ragtag, undisciplined volunteers at the front line. Most are youths from the most die-hard revolutionary neighborhoods of Tripoli, like Souq al-Jomaa or Tajoura, strong on zeal to kill some Gadhafi supporters and weak on training on how to do so.

The amateur Tripoli fighters get lost in the neighborhoods rolling up and down Bani Walid's confusing mountain ravines. Behind the front lines, frustrated fighters turn blame on the Bani Walid Brigade, units of city residents who are fighting alongside them but whose loyalties some of them suspect.

The new leadership is facing a tough fight uprooting the remnants of Gadhafi's regime nearly four weeks after the then-rebels rolled into Tripoli on Aug. 21 and ousted the now fugitive leader. Bani Walid, southeast of the capital, is just one holdout. Fighting is also raging at Sirte, Gadhafi's hometown on the Mediterranean coast. The regime stronghold of Sabha lies hundreds of miles away in the southern deserts, and there are others deep in the central deserts like the cities of Houn and Zallah.

The battle at Sirte, launched Friday, has also been fierce, but there the revolutionaries have been more organized and have made slow progress.

Most of the fighters besieging Sirte are from Misrata, a city further northwest along the coast that survived a brutal weeks-long siege by Gadhafi forces during the civil war. That conflict left them battle-hardened and savvy on the tactics of urban fighting. Regular truckloads of fuel and food arrive from Misrata to keep the fighters supplied outside Sirte.

"We deserve our reputation," said Ali el-Hani, a Misrata native leaning back against his pickup truck mounted with an anti-aircraft gun.

The past three days, they have battled block by block into the western side of Sirte, along the beach and along a eucalyptus tree-lined main avenue parallel to the coast. Other fighters in the low hills to the south have been drumming Gadhafi strongpoints in the flat plain of the city below with rockets and mortars. At least two dozen fighters were killed Saturday, but commanders say they gain ground each day. Another revolutionary unit from Benghazi _ further to the east _ claimed to be fighting its way to Sirte's eastern side to open up a second front.

Late Sunday, Gadhafi spokesman Moussa Ibrahim charged that revolutionary fighters have killed "hundreds every day." He told the Syrian Al-Rai TV station, which has become the Gadhafi mouthpiece, "Sirte is the symbol of resistance in Libya." He did not say where he or Gadhafi were.

Bani Walid, perched in the mountains 90 miles (140 kilometers) southeast of Tripoli, is far tougher to besiege.

A desert valley, called Wadi Zeitoun, runs through the center of the city, dividing it into north and south. In the southern part, loyalists command the heights of 100-foot-high escarpments overlooking the valley. Revolutionaries moving in through the city's northern half have reached the edge of the valley several times in the past few days, only to be pummeled by gunfire, mortars and rockets from the other side.

Each time, they retreat back to the relative safety of Wadi Dinar, at the city's northern entrance. The loyalists inside are believed to have received reinforcements and weapons through desert valleys that connect to other Gadhafi-controlled areas.

"Most of the guys here are not from here so it is a big challenge for us to fight," said Walid Turkey, a 28-year-old fighter from Tripoli. "We don't know the streets, and we're learning the makeup as we go along. This causes confusion and chaos."

At Wadi Dinar, the fighters rest, regroup and drink tea, decked out in their versions of revolutionary gear: baggy camouflage pants, berets and sunglasses _ or, in a more Islamic-chic version, beards with no mustaches and Palestinian-style kaffiyah scarves. When news emerges from the front line of any success _ a captured loyalist or piece of weaponry _ they shoot in the air in celebration. When frustration is high, they break into arguments with each other.

One group, rolling hash joints and relaxing on mattresses on the ground, fumed about their allies, the Bani Walid Brigade, made up largely of members of the Warfala tribe, which dominates the city they are besieging.

Some are convinced the Warfala fighters are secretly helping the city's defenders. One fighter swore that he saw a Warfala fighter feeding information to cousin, another said a Warfala fighter made him let go a loyalist he caught. Their accounts could not be independently confirmed _ but there was a definite bitterness among the city boys of Tripoli against their mountain allies.

"After today there is no Warfala and no Bani Walid," barked Abdel-Ghafar Marwan, a 28-year-old from Tripoli's Tajoura district. "They betrayed us and we don't want them to fight with us."

More Tajoura fighters pulled up Saturday night with a tank they said was captured during Tripoli's downfall. On Sunday, they posed for pictures on the tank and boasted more tanks were on the way.

Dr. Ehab Agha said two revolutionary fighters and one pro-Gadhafi soldier were killed and 15 wounded in the day's fighting.

After Friday's defeat, the NTC military _ which is somewhat more organized than the irregular fighters _ pulled back to re-attack later with more force, said Nasser Abu Zaid, 52, a representative from the council. "The Gadhafi force is too strong, fighting with weapons that we can't match."

Sunday afternoon, mortars and rockets rained down on the revolutionaries' position at the northern entrance. The irregular fighters fired back with rocket-launchers and anti-aircraft guns, then charged into the city for another push to Wadi Zeitoun.

Smoke rose from the city. Two ambulances rushed out carrying a revolutionary each.

Abu Zaid seemed unbothered by their unorganized fighting style.

"The revolutionaries have lots of passion," he said. "Yes, it's chaotic but this is war."

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Associated Press writer Ryan Lucas in Sirte contributed to this report.