"There are a total of 14,000 at-risk targets protected by police forces using 18,000 officers. There are more than 550 people protected... and more than 2,000 officers used for this task," the ministry said in a statement.

A national security committee met earlier on Thursday after Ansaldo Nucleare boss Roberto Adinolfi was injured in the shooting, reminiscent of multiple attacks carried out by political militants in Italy in the 1970s and 1980s.

The committee meeting "underscored the need to extend surveillance and investigation work so as to neutralise the risk of subversive acts which could further raise tensions" linked to the economic crisis, the ministry said.

Security has already been stepped up around prosecutors and high-profile personalities following the attack after the group claiming responsibility, the Informal Anarchist Federation, said it would carry out seven more.

"We do not want anything that would tarnish Rio's image," Roberto Alzir, deputy security secretary for Rio de Janeiro sate, told a press conference.

"With Rio+20, we are going to perfect ourselves for 2013 (the Confederations Cup), 2014 and 2016," he added.

Alzir said that since police began in 2008 to drive drug traffickers out of many favelas, the "Marvelous City" is already a lot more secure than in 1992 when it hosted the UN Earth Summit with army tanks pointing their guns toward the shantytowns.

"In 1992, there were 64.7 homicides for each group of 100,000 inhabitants in the city and last year, this was down to 24.1," a rate which keeps dropping, he added.

Officials said the security challenge for the landmark June 20-22 summit would be met through close cooperation between civil and military police.

Specific targets would be set, with bonuses of up to $4,500 every six months for police officers who meet them.

One of the targets is to get "adequate crime rates" in 2014 lower than 100 homicides for each group of 10,000 residents, Alzir said.

The number of police deployed in the streets from June 13 to 22 will be doubled, with 3,000 additional personnel daily.

The Rio+20 gathering, the fourth major summit on sustainable development since 1972, is to be attended by 115 global leaders and 50,000 participants from around the world, including corporate executives and representatives of various social movements.