THEY'RE easy to pick out at Arlington National Cemetery, usually kids looking down at their phones while the rest of the tour groups amble by - headed for the Tomb of the Unknowns or the grave of President John F. Kennedy.

The nation's war dead stretch for rows on rows, but they're looking down at their phones, trying to catch small little imaginary creatures called Pokémon.

And the cemetery has had enough of it.

"We do not consider playing 'Pokémon Go' to be appropriate decorum on the grounds of [Arlington National Cemetery]. We ask all visitors to refrain from such activity," the cemetery's Twitter account said Tuesday afternoon.

The game, a mobile app called Pokémon Go, was released July 6 and, like a fictional zombie apocalypse, has spread at an unprecedented rate.

The premise is simple: The player's digital avatar has to collect Pokémon, but to do so, the play has to explore the actual world as the virtual Pokémon world has been overlaid atop it using Google Maps data.

The mixture of real world locales and fictional creatures has led people to collect Pokémon in places where playing a game might be inappropriate, including the U.S. Holocaust Memorial Museum and the former site of the Auschwitz concentration camp in Poland.

The Holocaust museum has since asked attendees to refrain from playing the game when walking through its exhibits.

Arlington National Cemetery is the final resting place for more than 400,000 veterans and their families, according to the cemetery's website.

The cemetery holds funeral services Monday through Saturday at a rate of 3,000 per year. Many of the fallen from the United States' recent wars in Iraq and Afghanistan are buried in Section 60, their graves often adorned with their photos, notes from loved ones and empty beer bottles left by comrades.

The cemetery, in addition to discouraging Pokémon Go playing, also frowns upon running, bicycle riding and horseplay throughout its grounds.