Philadelphia police are investigating a threatening letter sent to Philadelphia's African American Museum on Arch Street in Center City.
According to the Associated Press, the anonymous letter threatened violent acts against the museum during the Democratic National Convention from July 25-28. Authorities said the letter referenced an unnamed group, possibly a white supremacist organization, that intends to carry out the attack, NBC10 reports.
Located at 7th and Arch Streets, the museum was founded in 1976 as the first institution funded and built by a major city to feature and exhibit the heritage of African-Americans.
On the night before the convention begins, the museum is scheduled to host an event celebrating its 40th anniversary.
Museum president Patricia Wilson Aden said the museum will remain open to the public pending the outcome of a police investigation.
"We are grateful for the quick response of law enforcement," Aden said in a statement. "This is an ongoing investigation and we are not at liberty to discuss details or make comments.