TRIPOLI, Libya — Facing little resistance, revolutionary fighters captured the airport and other parts of a southern desert city that is one of the last remaining strongholds of Moammar Gadhafi's forces Monday, even as military offensives stalled to the north.

The capture of Sabha would be a welcome victory for Libya's new rulers, who have struggled to rout forces loyal to Gadhafi a month after sweeping into Tripoli and forcing the ousted leader into hiding. He has not been found.

A push to capture Gadhafi's hometown of Sirte and the mountain enclave of Bani Walid has stalled as well-armed forces loyal to the fugitive leader fight back fiercely with rockets and other heavy weaponry. Libya's new rulers have frequently claimed gains only to find their forces beaten back.

A force of three southern brigades pushed its way into Sabha, deep in the Sahara Desert, on Monday.

"Our flags are waving there over the airport and other parts of Sabha," Col. Ahmed Bani, the military spokesman for the transitional government, told reporters in Tripoli.

The airport is about four miles from the center of Sabha, 400 miles (650 kilometers) south of Tripoli.

Hassan Moussa Tabawi, a spokesman of three southern brigades that led the takeover of Sabha, told The Associated Press that revolutionary forces have control of most of the city but still face pockets of resistance in a few central neighborhoods occupied by Gadhafi loyalists and Gadhadhfa tribe.

"The airport is totally secure and many residential neighborhoods have raised the liberation flag," he said in a telephone interview from Sabha. The two sides clashed on Sunday night, but he said the anti-Gadhafi fighters planned to take the rest of the city on Tuesday morning.

Before the arrival of the new government's forces, he said, Sabha residents tried to rise up several times over the past seven months but were besieged by Gadhafi troops.

"People were very happy to see us," Tabawi said.

Salam Kara, the Benghazi-based spokesman for Sabha's local council, said revolutionary forces also seized an old fort as well as a convention center and a hospital inside the city.

"It is a great achievement by the rebels from all over the south and led by the rebels from inside of Sabha," he said. "The resistance is not strong because Sabha's rebels have been holding protests for a long time and just needed help from outside."

Revolutionary forces have been sweeping through isolated towns in the rocky wasteland south of the Mediterranean coastal area where most of Libya's more than 6 million population live, in a bid to establish complete control.

Sabha could become a rallying point.

Tripoli's fall in late August — after a six-month civil war with NATO airstrikes aiding the rebels — marked the collapse of Gadhafi's nearly 42-year rule, but hopes that remaining pockets of resistance would be captured quickly were dashed when several offensives were repelled by die-hard Gadhafi loyalists.

Many also have speculated that the leader and his sons and other allies are hiding in the areas still under their control, some suggesting Gadhafi could be in the desert south of Sabha.

Sporadic battles also broke out over Gadhafi's hometown of Sirte and the mountain enclave of Bani Walid.

In Sirte, the two sides traded rocket and gunfire, sending up clouds of white smoke, before the fighting ebbed in the afternoon in what has become a daily pattern — the fighters push into the city in the morning but withdraw at night, forcing them to battle their way in each day.

"We can't stay at night in the city because Gadhafi cut the electricity and they know their own city," revolutionary fighter Lotfi al-Amin said. "We stay outside and then push in."

Al-Amin, a 37-year-old former postal worker who is now the head of a sniper unit, said the fighters also were concerned about a number of families from the city of Misrata who had been living in a Sirte neighborhood and were trapped.

He claimed Gadhafi's forces surrounded the neighborhood and killed five boys they kidnapped.

"The first thing we have to do is get the Misrata families out, then we can use all the firepower we have," he said.

Pro-Gadhafi fighters also fired anti-aircraft guns at revolutionary forces holding the northern gate of Bani Walid, another loyalist stronghold, for a second day Monday, as frustration with weeks of halting advances grows among the former rebel ranks.

The official, trained military forces of the National Transitional Council, Libya's interim government, 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 bands of ragtag, undisciplined fighters on the front line. These include fighters as young as 18 who spend hours smoking hashish, shooting at plastic bottles, arguing with one another and sometimes just firing wildly into the streets out of apparent boredom.

Revolutionary commanders were meeting with the leaders of the rebel brigades on Monday to try to rein in the chaotic fighting and organize ranks before a new push on the town, military spokesman Tarek Hadoud told the AP.

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When they decide to enter the town, they charge in half a dozen pickup trucks, only to retreat a short while later.

On Monday, three of their cars rode right into an ambush by Gadhafi forces on a street none of the outsiders was familiar with. One of their fellow fighters, Wassim Rajab, said he heard from comrades that four of them were killed.

Describing another typical attempt, fighter Lutfi al-Shibly from Libya's western mountains, said, "We entered the city, 600 meters from the city center, but we didn't have enough forces, so we lost the position and had to retreat."

Al-Shaheibi reported from Benghazi. Associated Press writers Ryan Lucas in Sirte, Hadeel al-Shalchi in Wadi Dinar and Maggie Michael in Cairo contributed to this report.