Someone phoned in racist threats to an employee of the Martin Luther King Jr. National Historic Site in Atlanta last month, the day before a gunman killed nine black worshippers in a South Carolina church, the National Park Service said Thursday. Bill Reynolds, a spokesman for the Park Service, said the threats were received through voice mail messages left for the King site employee June 16.

Although the messages were not “death threats,” Reynolds said the matter was being reviewed. “Because of the ongoing investigation, we are not able to provide specific information about the content of the threats,” the spokesman said in an emailed statement.

The Park Service did not say whether it believes the threats were connected to Dylann Roof, the 21-year-old white Columbia, South Carolina, resident charged with gunning down the churchgoers during a Bible study meeting at Mother Emanuel African Methodist Episcopal Church in Charleston on June 17. Roof has been indicted on state murder and weapons charges and 33 counts of federal hate crime charges.

Reynolds said King site visitors were safe after the reported threats. “The National Park Service has taken appropriate measures to address the safety and security of our visitors, employees and facilities,” he said, while also declining to discuss those measures in detail.

A call for comment to the Martin Luther King Jr. Center for Nonviolent Social Change, a nonprofit that runs a civil rights museum as part of the national historic site, was not returned on Thursday.

The Park Service confirmed the King Center threats on the same day that officials of the historic Ebenezer Baptist Church discovered four Confederate battle flags had been left on church grounds. Police said they were reviewing church surveillance video that shows two white males placing the rebel flags on the property early Thursday morning, several local media reports said.

King, the assassinated civil rights icon who co-pastored the Ebenezer Baptist Church on Auburn Avenue in the 1960s, stood against the Jim Crow segregation and white supremacy that the flag had come to symbolize during the civil rights movement in the Deep South. The church is also part of the national historic site.

The flags discovered at Ebenezer Baptist Church were placed below a “Black Lives Matter” poster on the path to the visitor hall of King Center, and on a corner near the church. Another grim moment from the Atlanta church's past occurred June 30, 1974, when King's mother, Alberta Williams King, was shot and killed inside the church. Her assailant received a life prison sentence and died in 1995.

In what seemed to be an acknowledgement of the Confederate flag incident at the church Thursday, Bernice King -- the youngest daughter of Martin Luther and Coretta Scott King, who is also CEO of the King Center -- urged her Twitter followers to express love in the face of hate.