London's Tate Modern says a vandal has damaged a mural at the gallery by modern American master Mark Rothko.

Tate says a visitor defaced the mural, one of Rothko's Seagram series, "by applying a small area of black paint with a brush to the painting."

A photograph posted on Twitter by a gallery visitor showed words, including the name Vladimir, scrawled in the corner of the painting. The gallery, which attracts 5 million visitors a year, was briefly closed Sunday after the incident.

Tate Modern says police are investigating.

Rothko, who died in 1970, is renowned for his large abstract paintings featuring bold blocks of color.