Vials of blood found in package addressed to Trump at RNC's DC headquarters: Sources

The U.S. Secret Service is investigating a package found at the Republican National Committee's Washington, D.C., headquarters Wednesday.

The package was addressed to former President Donald Trump and allegedly contained vials of blood, sources familiar with the matter told ABC News.

The U.S. Capitol Police said they temporarily locked down the location around 7:45 a.m. after they received a call about the package.

Officers arrived on the scene around 7:50 a.m. after the package was found, according to police.

Secret Service members were called in to assist with the investigation, the agency said.

"The package contained vials of liquid suspected to be blood, and the packaging and contents were collected for further testing," USSS Washington Field Office Special Agent in Charge Matthew Stohler said in a statement.

The Secret Service did not officially disclose who the package was addressed to, but Stohler said it was "addressed to a Secret Service protectee."

Police lifted the lockdown shortly after the package was removed. An investigation into the incident and the package's source is ongoing, according to police.

The RNC thanked officers for their swift work.

"The lockdown has been cleared and staff has resumed their office duties because we remain unintimidated and undeterred in our efforts to elect President Trump to the White House," RNC Chairman Michael Whatley said in a statement.

During her daily briefing, White House press secretary Karine Jean-Pierre said the incident was "concerning" and condemned political threats.

"That has no place in our politics," she said.

ABC News' Beatrice Peterson contributed to this report.