The headquarters of the Republican National Committee were evacuated early Wednesday after a package containing two vials of blood was delivered to the building.

RNC Chairman Michael Whatley said the vials of blood were sent to the organization's headquarters, prompting a police lockdown of the building. In a statement, he called it a "revolting attack."

The RNC, the parent organization of the Republican Party, is playing a major role in the campaign of former President Donald Trump, who will face Democratic incumbent Joe Biden in the Nov. 5 election.

White House Press Secretary Karine Jean-Pierre called reports about the blood vials "concerning" during her regular briefing with reporters.

She said the White House condemns "any political violence, threats or intimidation."

Authorities initially closed off one street and directed staff and other personnel to avoid the area, which is close to the U.S. Capitol building. By midmorning, employees were re-entering the offices, and police were leaving the scene, according to a Reuters witness.

"The source of the package and its contents will be further investigated," U.S. Capitol Police said in a statement.