LONDON - A painting by Russian-American artist Mark Rothko was defaced by a visitor to London's Tate Modern museum on Sunday and a spokeswoman said police were investigating.

According to a statement from the popular gallery located on the River Thames, the incident took place at 15:25 p.m.

"Tate can confirm that ... there was an incident at Tate Modern in which a visitor defaced one of Rothko's Seagram murals by applying a small area of black paint with a brush to the painting," it added.

Rothko, considered one of the 20th century's most important artists and whose works sell at auction for tens of millions of dollars, was commissioned to paint the Seagram Murals in the 1950s for the new Four Seasons restaurant in New York.

Several of them ended up in the Tate collection after they were given as gifts, and Tate describes the famous series of soft-edged, colored rectangles, as "iconic".

Tim Wright wrote on the Twitter micro-blogging site that he witnessed the incident and posted a photograph of the damaged canvas online.

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