A plaque installed in honor of murdered opposition politician Boris Nemtsov has been removed less than a week after it was put up on his house in central Moscow, the Ekho Moskvy radio station reported Tuesday.

“It is not known who removed it,” the Ekho Moskvy radio station said, posting photographs from Facebook of the building without the plaque. “No official statements were made on this matter.”

The Facebook user who posted the photos, Tatiana Tikhonovich, included a screenshot of a post made by pro-Kremlin activists who claimed to have removed the plaque early Tuesday.