RIO DE JANEIRO — Soldiers and police crouching behind armored vehicles trained their rifles on dozens of entrances to a sprawling slum Saturday, apparently preparing to invade and try to push drug gangs out an area long considered the most dangerous in Rio de Janeiro, a city set to host the 2016 Olympics.

A delicate calm held after a night that saw intense exchanges of gunfire, filling the dark sky with bright streaks as bullets whizzed into and out of the Alemao slum complex – an area near the highway to the international airport that is known locally as the “Gaza Strip.”

Soldiers in camouflage, black-clad police from elite units and regular police held their ground at the entrances to the complex, a grouping of a dozen slums that climb up gentle slopes where more than 85,000 people live, according to the Brazilian government.

The standoff comes after a week of intense and widespread violence in Rio, with dozens of mass robberies of motorists on key roadways, more than 100 cars and buses set on fire and at least 35 deaths, mostly suspected traffickers.

Authorities say the gangs are protesting against a 2-year-old police campaign that has pushed the criminals out of slums where they have long ruled with impunity. It’s an effort to secure Rio before the city hosts the finals of the 2014 World Cup and the 2016 Olympics.

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 – and he and other officials say now is the turning point in that effort.

Vila Cruzeiro, a slum neighboring the Alemao, was occupied by police forces Thursday. Video from Globo TV’s helicopter showed about 200 heavily armed men running from Vila Cruzeiro across the green hilltop that separates it from Alemao.

“Sooner or later, we’re going to get these criminals,” Rio state Public Safety Director Jose Beltrame told the Globo television network Friday night. “The anguish of Rio’s citizens is my anguish. But we have our objectives and we cannot retreat.”

Many Alemao residents spent the night away from home for fear of being caught in crossfire. The death count since Sunday, when the violence began, climbed to 35 by Saturday morning, with four more people confirmed dead. About 123 have been detained and 76 arrested, said police spokesman Henrique Lima Castro Saraiva.

The chief Brazil photographer for the Reuters news agency, Paulo Whitaker, suffered a non-life-threatening bullet wound in the shoulder. The source of the shot was not immediately clear.

The human rights organization Amnesty International complained that police have been too heavy-handed.

“The police response has put communities at risk,” said Patrick Wilcken, Amnesty International’s Brazil researcher, in a statement. “The authorities must ensure that the security and well-being of the broader population comes first and foremost in any operation carried out in residential areas.”

Many Rio residents seemed to welcome the aggressive stance, however, applauding as armored vehicles rolled by and voicing hope that a new push would reclaim areas of their city that had been lawless for years.

An information hot line where residents can pass on tips about the movements of drug traffickers received a record number of phone calls over the last few days, the coordinator, Zeca Borges, told the Rio’s O Globo newspaper.

“People are supporting the operation,” he said.

A mother pushing her 1-year-old daughter in a stroller alongside Ipanema beach said she often thought police were too aggressive, but this time, she supported the law enforcement takeover of the slums.

“I’m not one of these people who says you just have to shoot the criminals,” said Flavia Tavares de Almeida. “But we have this beautiful city, with 99.9 percent of people who are just workers, and want to live their lives, and are being terrorized by these traffickers.”

Cabral said police taking the Vila Cruzeiro slum and poised to enter Alemao was a sign of a new Rio.

“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.”