Rebel fighters in the besieged city of Misrata have won a significant victory by retaking key buildings that had been occupied by Muammar Gaddafi's forces for more than a month.

The Tameen office block, the city's tallest building, with a view across Misrata, was captured after bombardment by rebel forces. Numerous snipers were either killed or captured. Several other buildings nearby were also cleared, leaving the rebels in control of the northern end of Tripoli Street, the city's main thoroughfare, which Gaddafi's forces have been desperate to capture. Snipers had caused havoc in the city after they were sent in on 19 March, picking off civilians and rebels at will, as well as firing missiles from the roof of the buildings into civilian areas.

On Friday morning, rebel forces were moving freely around the area near the Tameen building, which is littered with abandoned tanks. Firefighters were cleaning the streets.

"In this area, all the families had to leave because of the threat of the snipers," said Hadi Tantoun, a journalist and rebel. "Capturing this building was very important."

The snipers had been cut off from the rest of Gaddafi's forces for a week or more, unable to receive supplies. Entering the Tameen building through the reception, strewn with debris, it was possible to get a glimpse of how they had been living.

Mattresses and blankets indicated that several snipers had been sleeping in the stairwell on the first floor, relatively safe in the centre of the building. Their cooking pots still stood in the atrium area nearby. The once-smart offices on the sides of the building, whose tenants were mostly insurance agents, had been trashed by the snipers, with files on the floor and upturned sofas. In some offices, cabinets had been pushed against windows for protection. Many glass panes had been shattered by rebel fire.

"Every night we attacked them with our RPGs [rocket-propelled grenades] and Kalashnikovs," said Abdullah Hafiz, 24, a member of the "City Centre" rebel cell that finally liberated the building. "They killed a lot of civilians." On higher floors there were empty tins of tuna and tomato paste, blankets, mattresses and sandals, and a few discarded green uniforms.

According to rebel fighters, the few dozen snipers that still occupied the building this week had changed into civilian clothes before trying to escape down Tripoli Street on Thursday, towards their main base in the vegetable market. A sniper's chair had been placed under a small window, which offered a view down the main street. Dozens of spent bullet shells and cigarette butts littered the floor around the chair.

In an office that had belonged to an architect there were graffiti written in green ink-– Gaddafi's colour – in Arabic. It read: "If we survive, we are warning you gays and dogs. We will not forgive anybody from Misrata. We will fuck your daughters and your wives." One of the rebels had already penned a riposte: "Misrata is strong. We will win in the end."

On the top floor, several Gaddafi soldiers had been sleeping on dirty mattresses next to the elevator works. A torn photograph of a woman – a wife of one of the snipers perhaps – lay on the floor. On the roof there were thousands of spent bullet shells, and numerous discarded cases of anti-tank missiles that had been fired into the city.

Up here the snipers would have had a clear view of the city, and everything that moved down below. They would have seen the destruction in the area nearby – buildings pockmarked by gunfire, featuring gaping holes where shells had struck, blackened by smoke. Glass and tyres and twisted metal on the streets.

At the foot of the building lay the body of a sniper, covered with a blanket. It had been burned. One of the rebels said that if Gaddafi's forces could not get their dead back to base, they set them on fire.

A few civilians ventured cautiously on to Tripoli Street, which housed some of the city's best coffee shops, several banks and the Italian-built hotel where Mussolini once stayed.

A rebel with a loudhailer warned them not to try to enter any of the shops: "This is not your property. Even if it is government property, it is for all the people."

He then cleared the area, saying it was still dangerous. The rebels had learned their lesson on Thursday night.

After taking over the Tameen building, they dropped their guard while celebrating.

Several fighters were killed, prompting scenes of grief at the main hospital, where brothers, fathers and colleagues of the victims wept and swore to avenge them.

In a sign that the regime was giving up on Misrata, the Libyan deputy foreign minister, Abdul Ati al-Obeidi, said yesterday that the army may withdraw and let surrounding tribes deal with the rebels. He also said the use of Predator drones – announced by US defence secretary, Robert Gates, on Thursday – would be a crime against humanity.

John McCain, the US senator who arrived in Benghazi yesterday to meet rebels, called for increased military support for the opposition, including weapons, training and stepped-up airstrikes, in a full-throated endorsement of the opposition in its fight to oust Gaddafi. A day after the US began flying armed drones to bolster Nato firepower, the top Republican on the Senate armed services committee said the US and other countries should recognise the opposition's political leadership as the "legitimate voice of the Libyan people".

The White House disagrees, saying it is for the Libyan people to decide who their leaders are.