SAO PAULO, Oct 21 (Reuters) - The Brazilian government said on Tuesday it has put an environmentally rich area of the Amazon rainforest under federal protection, creating a reserve larger than the U.S. state of Delaware.

The new reserve, called Alto Maues, has 6,680 square km (668,000 hectares or 1.65 million acres) of mostly untouched forests that are not known to have human presence, the Brazilian Environment Ministry said.

Declaring a federal reserve means forest clearing and similar development are forbidden.

Putting large areas of mostly intact rainforest under federal protection is one of the tools the Brazilian government has to combat deforestation and reduce its greenhouse gas emissions.

The creation of these reserves is part of the country's climate policy. Deforestation is the main cause of carbon emissions in Brazil, unlike most countries where the burning of fossil fuels leads emissions.

The decree creating the reserve was eagerly expected by environmental groups.

"This is essential to protect unique Amazon species, such as some types of primates," said Mauro Armelin, a conservationist working for the local office of the World Wildlife Fund (WWF).

WWF said at least 13 species of primates and more than 600 species of birds are found in the Alto Maues area.

The organization, however, said that declaring the area a federal conservation unit does not guarantee its integrity.

Amazon deforestation went up in Brazil last year for the first time since 2008, as illegal loggers and land grabbers increased their activities, challenging government controls.

The destruction of the world's largest rainforest rose 29 percent in 2013 from the previous year, totaling 5,891 square km (3,360 square miles). (Reporting by Marcelo Teixeira; Editing by Cynthia Osterman)