(Reuters) - Racist graffiti was painted in the parking lot of a Tennessee social justice center that hosted giants of the 1960s U.S. civil rights movement, such as Martin Luther King, Jr. and Rosa Parks, it said on Tuesday.

Slideshow ( 3 images )

The Highlander Research and Education Center, whose main office burned down last week, was home to innumerable documents, recorded speeches and artifacts from the movement that were lost in the fire, it said on its website.

It described the graffiti only as a “white power” symbol painted on the parking lot.

“While we do not know the names of the culprits, we know that the white power movement has been increasing and consolidating power across the south,” the center said in a statement on Tuesday. “Now is the time to be vigilant.”

Friday’s fire was less than a week after another fire police say was race-driven arson at a Southern California mosque, where racist graffiti was left in the parking lot.

No one was injured in either fire.

The Jefferson county sheriff’s office is investigating the Highlander Center fire as a possible crime, broadcaster NBC and other media have said.

A sheriff’s spokesperson was not immediately available to comment to Reuters early on Wednesday.

The Highlander Center helped organize the Montgomery, Alabama, bus boycotts of 1955 that were among the first major civil rights protests of the movement in the United States.

Protesters, mostly black residents, refused to ride city buses in a bid to defy racial segregation, after Parks was arrested for refusing to give up her seat to a white person.

The center also helped found the Student Nonviolent Coordinating Committee, a youth movement that worked with Martin Luther King Jr.’s efforts to ensure voting rights and social justice for minorities, it said on its website.

(This version corrects center’s name to “Highlander” throughout, deletes incorrectly described quote, paragraph 9)