FBI and US Air Force agents have raided the homes of a man who runs a website about the top secret military base in Nevada known as Area 51.

Officers entered the properties of Joerg Arnu in Las Vegas and the town of Rachel, which is close to the defence facility, earlier this month as part of a joint investigation, authorities have confirmed, but gave no further details.

The blogger operates a site called Dreamland Resort which focuses on Area 51, an air force base about 120 miles northwest of Las Vegas where testing is conducted on classified military aircraft.

Started by Mr Arnu in 1999, it includes satellite images of the base; articles on test flights, “black projects” and UFOs; drone videos of locations around Area 51 and details on scanner frequencies.

Confirming the raids, Lt Col Bryon McGarry, a spokesman for Nellis Air Force Base in Las Vegas, said in a statement to the Las Vegas Review-Journal: “This is an open and ongoing law enforcement investigation between the Las Vegas FBI and Air Force OSI (Office of Special Investigations).”

In a news release posted on his website, Mr Arnu said: “I believe the search, executed with completely unnecessary force by overzealous government agents was meant as a message to silence the Area 51 research community.”

He said each of his homes had been raided on 3 November by up to 20 agents “in full riot gear”.

The raids happened while Mr Arnu was in his Rachel home and his girlfriend in the Las Vegas one, and he said they were both “detained and treated in the most disrespectful way”.

He added: “My girlfriend was led out into the street barefoot and only in her underwear in full view of our neighbours.

“I was led outside, handcuffed and only in T-shirt and sweats in sub-freezing temperatures.

“Despite my repeated requests for an explanation, I was only told that the search was related to images posted on my Area 51 website.”

During the raid, Mr Arnu claimed that all of his “laptops, phones, backup drives, camera gear and my drone were seized”.

He estimated the damage to his home at $5,000 (£4,206) and the value of the confiscated equipment at $20,000 (£16,823).

He claimed there were 40 pages missing from the search warrant he received and the case file was sealed, preventing him reading about it.

Mr Arnu went on: “In an effort to defuse the situation I have removed some material from my Dreamland Resort website although I believe that it was legally obtained and legal to publish.

“I am not sharing anything on my website that cannot be found on dozens of other websites and news outlet publications.

“Considering how this went down I have no intention of removing any more material unless ordered to do so by a federal judge.”

Area 51 has long been a focus of UFO and alien conspiracy theories, only enhanced by its secretive role.

The nearby state route 375 was even officially dubbed the Extraterrestrial Highway in 1996.

But Mr Arnu is dismissive on his website of UFO stories.

He states: “In reality, anyone who spends some time investigating Area 51 will quickly understand that what goes on there is very earthly in origin and has nothing to do with ‘ET’.

“It becomes apparent that the abundant UFO folklore is nothing but a welcome smokescreen, a distraction from the real purpose of the base, research and development of all sorts of black projects.”