Rio De Janeiro - Brazilian military forces took fire from drug-gang members holed up in a massive slum complex Friday, but stood their ground, trapping the traffickers inside.

About 800 troops are supporting a massive police operation at the Alemao complex of shantytowns, an operation that came just a day after police took over a separate slum.

Authorities are not publicizing their plans, but it appears an invasion of Alemao, Rio's most dangerous slum, is imminent.

"This is not the moment to circumvent risks, but rather to confront risks," said Brazilian Defense Minister Nelson Jobim, who traveled to Rio to meet with the state's governor and top security officials.

Military spokesman Enio Zanan said that soldiers have been taking fire from drug-gang members hiding in the large complex but did not return it out of fear of hitting civilians.

"These men are prepared, and won't return fire at random," he said. "There are innocent people in the community where these guys are hiding."

Zanan said the standoff has no set time or date to end and the troops are ready to stand around-the-clock guard as long as needed.

Federal and state police officers, meanwhile, conducted door-to-door searches and patrols within the Vila Cruzeiro slum. The area was taken by officers Thursday afternoon during a five-hour operation using armored vehicles and assault rifles.

After armored vehicles had their tires blown out by gangs or were stymied by burning tires, police relied on personnel carriers equipped with caterpillar treads to roll over or push aside barriers and enter the fortified shantytown.

Officials trumpeted their victory Friday, hailing it as a sign of a new Rio.

The governor of Rio state, Sergio Cabral, said the moment was historic - for proving that no part of Rio was beyond the reach of the law, and for the unprecedented cooperation of the armed forces with police to bring peace to Rio, whose name has long evoked the violence of its lawless shantytowns.

"We have demonstrated to those who don't respect the law ... the pre-eminence of a democratic state governed by the law," he said. "Bringing peace to this population makes this a very important day for Rio."

Jobim called the unprecedented cooperation of the armed forces a "change in paradigm" that would assure "peace and the exercise of human rights" in Rio de Janeiro.

Slum residents, streaming out down steep, narrow alleys to jobs in the city below, had mixed reactions as officers approached them. Some ran away, and others stayed to welcome them and cooperate by showing their identification.

Marcilio Alves, treasurer of the residents association of Chatuba, one of the slums in the nearby Alemao complex of shantytowns, and whose son and ex-wife live in Vila Cruzeiro, said people were trying get back to their routines Friday.

But the community remained without electricity, as utility workers were afraid of going up the hillside to repair wiring damaged during the incursion. Residents were also nervous, because the police force's hold on the area was still seen as tenuous, and they were afraid that cooperating with law enforcement officials or talking to the news media would brand them as snitches if the gangs returned, Alves said.

"The police are saying they're going to bring order to the place, but who knows what will really happen," he said. "The traffickers, they're like a fever in a city that's sick: They go away but they come back."

More than 80 abandoned motorcycles and at least one body were found during the search Friday morning, reminders of the gang's quick retreat the day before to the Alemao complex - among the best-defended gang turf in the city.

Nearly 200 people have been arrested or detained since the start of the widespread violence Sunday, said police spokesman Henrique de Lima Castro Saraiva. More than 96 buses and cars have been burned on major roadways, many motorists have been robbed and police outposts have been shot in the city that will host the final match of the 2014 World Cup as well as the 2016 Olympics.

It is unclear how many people died in Thursday's violence, but police said at least 28 have been killed since Sunday. Three police officers have been injured so far.

The military support was authorized late Thursday by President Luiz Inacio Lula da Silva to help police keep their hold on the occupied area and prevent gang members from escaping.

"Anything we can do for Rio, we'll do," Silva told reporters from Guyana, where he is attending a summit of the Union of South American Nations. "It is not acceptable that 99 percent of well-meaning, hardworking people who want to live in peace are affected by violent groups."

Zanan said the military troops designated to help are trained in suppressing conflict and have served in Haiti. Two other battalions of 800 troops each could be deployed as needed over the next few days, he said.

About 3,000 police reservists and retirees who are able to take on desk duties have volunteered to join the effort, the police and firefighter association said in a statement.

Security officials declined to say if they would enter Alemao on Friday or if they would wait, invading the area sometime within the next six months, as had been planned earlier.

Brazil is trying to clean up the seaside city before the World Cup and Olympics. Over the past two years, authorities have established permanent police posts in 13 slums as part of an effort to bring basic services to the communities and rid them of violence related to drug trafficking.

"We took from these people what has never before been taken - their territory, their safe harbor," said Rio state Public Safety Director Jose Beltrame. "It's important to arrest them, but it's more important to take their territory."