The Brazilian Armed Forces have started patrolling key districts in Rio de Janeiro for the upcoming United Nations Conference on Sustainable Development (Rio+20) scheduled on June 20-22.

Brazil will host the summit, and have started patrolling the city. [File photo]

Marine troops have been stationed along main highways to the city, occasionally accompanied by vehicle support, according to the security force of the conference.

Coastal patrol has also been launched by the Brazilian Navy with a helicopter, a patrol ship, and fleet of smaller vessels deployed along the city's coastline.

As many as 8,000 Brazilian military troops are among the Rio+20's 15,000 security force, which is composed of personnel from the navy, marines, air force, police, fire department, civil defense and municipal guard.

Anti-terrorism and cyber defense units will participate in the security efforts as well.

Besides, Brazil has received foreign assistance in the area of intelligence security, authorities said.

The preliminary events will start Wednesday ahead of the Rio+20 summit, which will attract more than 100 heads of state and government.