Rio police backed by helicopters and armored vehicles invaded a shantytown complex long held by traffickers on Sunday, quickly taking over the key drug gang stronghold, a top official said.

Black-clad officers from elite police units entered the Alemao slum complex amid heavy fire, with TV images showing police and army helicopters flying low to support the men on the ground as hundreds of drug gang members tried to hold their position.

But the officers encountered less resistance than expected and claimed victory, saying police were controlling the shantytown complex although many gang members still remained inside.

"We won," said Mario Sergio Duarte, head of Rio state's military police. "We brought freedom to the residents of Alemao."

Officers on the ground, however, were saying they had not completely taken over the complex, and that gunmen were still fighting back. Gunfire could still be heard in the area.

"Without any doubt we know there are gang members hold up inside this slum still and we've got to go in and take them out," said one solider at the base of the slum who did not want to give his name because he was not authorized to speak to the media.

"Now it's time to be patient," Duarte said. "We've taken over the territory but it doesn't mean that we won't have confrontations with the gang members still inside. We have to be careful because they may be trying to set up traps for our men."

At least five police helicopters were buzzing atop the Alemao, helping provide intelligence on where the gang members might be.

Police and troops started moving up the slum inside armored vehicles as residents watched from their windows in shacks packed along steep hills. Massive tracked armored personnel carriers were moving in and out of the slum entrances on its southern edge, carrying soldiers with their faces painted.

High-caliber rifle casings littered the streets for three blocks around the slum, and bloodied bandages were scattered on the ground near entrances where soldiers and police crouched behind buildings aiming their rifles toward the slum.

Vehicles from the forestry service were seen moving around the shantytown complex, carrying soldiers to the jungle areas inside the slum to cut back trees and eliminate possible escape routes.

There were no initial reports of police officers injured on Sunday.

Duarte said large amounts of weapons, ammunition and drugs were seized in the operation, which came after a week of widespread violence in Rio, with more than 100 cars and buses set on fire and at least 35 deaths, mostly of suspected traffickers.

Hundreds of soldiers on armored vehicles were in place to support the operation, seen as a key move in a long-standing campaign to push criminals out of slums where they have long ruled with impunity.

Duarte said officers will enter each shack to try to find hidden gang members and to seize weapons and ammunition.

"We won't leave a place unchecked," he said. "We suspect that are a lot of people who are still trying to flee."

Authorities were asking residents to remain inside their homes and to cooperate with police. Many were thrilled with the police operation.

"Fantastic, this is exactly the thing we needed," said Ana Costa, a 48-year-old woman who lives a block from the slum in the Penha neighborhood, which is house to about 400,000 people.

"This community has been so violent for so long that I never thought that I would see this day," she said as at least three armored vehicles drove rapidly by her house. "I still have my doubts but I'm praying that peace has finally come here."

Hundreds of soldiers in camouflage and elite and regular police had been surrounding the Alemao since Saturday night, sheltering behind the armored vehicles. They had exchanged intermittent, heavy gunfire with gang members at many of the 44 entrances to the slum.

More than 1,000 police and soldiers had been prepared to storm the shantytown complex as about 600 armed gang members remained trapped inside. Authorities had been saying the invasion was inevitable if the gang members did not give themselves up.

"The gang members decided not to surrender," police spokesman Henrique Lima Castro Saraiva said Sunday, adding they "would not stand a chance" against the security forces.

The invasion came after Rio saw its calmest night in a week, with only one volley of gunfire heard overnight in the slum. Police said there was gunfire around 1 a.m., but after that mostly silence.

In the rest of the city, for the first time in more than a week there were no vehicles burned _ what had become a hallmark sign of the gang's bloody protest against a tough policing program.

In a week of widespread violence blamed on the gangs, authorities had already seized the Vila Cruzeiro slum, which was once thought virtually impenetrable. More than 200 armed gang members fled that offensive and ran to the nearby Alemao complex of a dozen slums that are home to at least 85,000 people, followed by security forces on Friday.

Saraiva had said the deadline for the gang members to surrender was "when the sun sets" on Saturday. He said the gang members were "exhausted, hungry, thirsty, stressed out" and had not been able to bring in more ammunition.

Rio de Janeiro's governor, Sergio Cabral, has vowed repeatedly to break the back of drug gangs that have ruled hundreds of shantytowns in the city of 6 million people.

The human rights organization Amnesty International complained that police had been too heavy-handed in their offensive, but many Rio residents seemed to welcome the aggressive stance. People applauded as armored vehicles rolled by and voiced hope that a new push would reclaim areas of their city that had been lawless for years.

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Associated Press writers Juliana Barbassa in Rio de Janeiro and Tales Azzoni in Sao Paulo contributed to this report.