Facebook said Tuesday afternoon that the removal of a controversial event page in which people were encouraged to storm famed Area 51 was "a mistake." The page has now been restored.

A check of the event page Tuesday morning shows it's no longer available after some 2 million people signed up. Its creator, Matty Roberts, posted this screenshot to his personal Facebook page, showing the note that it had been removed (Warning; Graphic language).

"Storm Area 51, They Can't Stop All of Us has been taken down by Facebook because content posted to this event went against our community standards. Repeated Community Standards violations can lead to your Page getting unpublished," the screenshot reads.

RELATED: Forget Area 51, you can storm this animal shelter and take their 'aliens'

RELATED: 'Storm Area 51' event creator breaks his silence

"I never got any reason behind the event being removed," Roberts reportedly told CNET, saying the page was meant as a joke.

Hours later, the event page was restored. 

"This was a mistake and the event page is now available again," a Facebook spokesperson told TEGNA. The spokesperson did not elaborate on the nature of the mistake.

What made the temporary removal additionally frustrating for Roberts is that he is using it to direct people to an actual festival he has set up for Sept. 20 in a non-classified, public area of Nevada.

The initial event called for people to "Naruto run" at 3 a.m. into the remote U.S. Air Force test area in the Nevada desert that has long been the focus of UFO conspiracy theories. The face-forward, arms-back running style is favored by characters in the anime series "Naruto."

"They can't stop all of us," the post joked. "Lets see them aliens."

That led the military to warn people not to try to enter the once top-secret Cold War site, which is posted and patrolled as part of the vast Nevada Test and Training Range.

After refusing for decades to acknowledge Area 51 even existed, the CIA declassified documents in 2013 referring to the 8,000-square mile installation by name and locating it on a map near the dry Groom Lake bed.

The base has been a testing ground for top-secret aircraft including the U-2 spy plane in the 1950s and later the B-2 stealth bomber.