Muscovites awoke to a surprise –- and highly unauthorized -- paint job on the crown of the 32-floor Kotelnicheskaya Embankment Building Wednesday morning. Someone or some group climbed to very top of the building’s spire, painted the hammer-and-sickle emblem blue and yellow, then planted a Ukrainian flag squarely atop the 577-foot-tall skyscraper. The stunt appears to be an act of solidarity with neighboring Ukraine, which is deeply embroiled in a bloody battle with pro-Russian separatists the West says Russia actively supports.

The paint job is the most daring show of pro-Ukrainian activists in the Russian capital yet. Russian security officials say they’ve arrested four climbers, or “hooligans” as they're calling them, caught with climbing gear. The climbers used a utility staircase to reach the top of the building and then reached the top using climbing gear, according to police. No one has come forward to claim responsibility for the stunt.

The Kotelnicheskaya Embankment Building is one of the “Seven Sisters,” a group of seven Stalinist-era high-rises in Moscow that Stalin himself commissioned at the end of World War II. Other Seven Sister skyscrapers include the Russian Foreign Ministry, Hotel Ukraina and the main building at Moscow State University. The Kotelnicheskaya Embankment Building is an apartment building.

It's not the first time one of the Seven Sisters has been scaled. Check out a pair of daredevil climbers scaling the Kotelnicheskaya armed with a helmet camera instead of spray paint: