The FBI has admitted to gathering secret intelligence about the annual Burning Man festival since 2010.

In response to a request under the 2012 Freedom of Information Act, the security service said its Special Events Management unit has kept files on festival-goers, known as 'burners' - to 'aid in the prevention of terrorist activites and intelligence collection'.

But the FBI's 16-page response to the question by Inkoo Kang is heavily redacted, with information about the technology being used to secretly gather the information being blanked out.

The revelation comes as the 29th Burning Man takes place in the Black Rock Desert in Nevada.

The FBI document describes the festival as a 'cultural and artisan event, which promote (sic) free expression by the participants'.

Scroll down for video

'Charcade'L Samuel Coniglio controls the flames by dancing at the Charcade during the Burning Man 2015 'Carnival of Mirrors'

Skeeball of flames: People play a game of flaming skee-ball at the Charcade during the Burning Man 2015 on Tuesday

The Man: The eponymous 'The Man' stands guard over this year's Carnival of Mirrors in the Black Rock desert of Nevada

Art: Participants interact with an art installation during the Burning Man 2015

The FBI said its involvement was 'even more critical in the light of the ongoing war on terrorism and the potential for additional acts of terrorism being committed in the United States.'

But later the FBI warns: 'The greatest known threat in this event is crowd control issues and use of illegal drugs by participants.'

The heavily-redacted document said that the Las Vegas FBI will work with all appropriate law enforcement agencies on the material it gathers.

The event is held in a remote area, branded Black Rock City, which is twelve miles from the nearest town, Gerlach, and 75 miles from Reno, Nevada.

MuckRock.com reported that Inkoo Kang submitted the FIOA request about he FBI's involvement in the annual event.

According to the FBI report, participants, who are into 'free expression', pay a fee to enter the area. 'Once inside, the participants access to the venues is unrestricted.'

Interactive: Burning Man 2015 attendees interact with an art installation, part of a week of festivities in the Nevada desert

Light-up bikes: Participants illuminate their bikes for travel at night on the Playa during this year's Burning Man

Serpent monster: People gather at the art installation Serpent Mother during the Burning Man 2015 on Tuesday as participants continued to arrive to the sold out festival

Participants gather at the base of 'the Man' on Tuesday. Participants are still arriving from all over the world for the sold-out festival

The FBI document, handed over in response to a Freedom of Information request, advises that the event is 'considered cultural and artisan' and promotes 'free expression'

The FBI said they would work with other agencies in the 'prevention of terrorism and intelligence gathering'

The FBI seems to believe that many of the participants at Burning Man enjoy taking illegal drugs

One redacted section of the 16-page document referred to the FBI Academy in Quantico, Virginia.

Burning Man, currently in its 29th year, begins on the last Monday of August and ends on the first Monday of September, for a week of festivities centered around art and alternative living.

Since money is effectively outlawed at the site, guests are urged to barter for commodities and many fans have already taken to social media offering to swap items such as crystals for festival tickets.

The entire campsite is temporary, and participants are required to bring everything with them, from food to tents and even furniture.

Every year, several massive 'temples' are built according to a theme, and on the last day, they are burned down in a ritualistic ceremony.

Adorable, her Playa name, rides a swing during the Burning Man 2015 'Carnival of Mirrors' arts and music festival in the Black Rock Desert of Nevada

Dan Drahos dances at the Robot Heart during the morning hours at the Burning Man 2015

Wilf Griese interacts with the art installation Compound Eye, one of what seems like an endless array of such installations at this year's Burning Man

Kentucky Sunshine, her Playa name, rides a rocking horse art installation in the desert on Tuesday

The FBI has been using the Burning Man festival in Nevada as a method of testing surveillance techniques

The FBI warned that crowd control and drug use are the most significant problems facing law enforcement

Many of those attending Burning Man were fans of 'free expression', according to the security service

People attending Burning Man have been warned that the weather can change quite rapidly in the desert

Despite the dangers, some people bring their children along with them to the desert festival

Visitors to Burning Man are warned by organisers about the dangers posed by dust storms

'Burners' use a range of ways of travelling around the festival site which is 12 miles from the nearest town

Some of those incorporate 'performance art' into their method of transport around the campsite