All federal facilities are on heightened alert for suspicious activity and have enhanced security procedures following a set of bomb scares across the country Wednesday, said Homeland Security Secretary Kirstjen Nielsen.

Nielsen also said the department is actively communicating with the National Network of Fusion Centers, which accept and process information provided by state and local agencies on criminal or terror-related issues then presents it to DHS as a threat overview.

"I condemn these cowardly acts in the strongest possible terms. Americans will not tolerate these types of threats, and we will not be intimidated," Nielsen said in a statement released Wednesday evening.

Top Democratic officials, including former President Barack Obama and former Secretary of State Hillary Clinton, were mailed suspicious packages that arrived Wednesday morning.

Packages were addressed to former Attorney General Eric Holder, former CIA Director John Brennan, billionaire and liberal donor George Soros, Rep. Maxine Waters of California, and Sen. Kamala Harris of California. Former Democratic National Committee Chairwoman Rep. Debbie Wasserman Schultz of Florida received a package at her office, which was used as the return address.

The packages sent to Obama, Clinton, Brennan, Holder, and Soros all contained bombs. The two others resemble those items but have not been confirmed by the FBI as containing explosives.

None of the packages mailed to officials across the country detonated.

The FBI has launched a national investigation — at President Trump's command — to determine who was behind the attacks.

“DHS and the U.S. Secret Service are closely coordinating with the FBI on the active investigation and are working with state and local law enforcement to provide updates on the evolving situation,” Nielsen said.

In addition, CNN’s New York office in Manhattan was also sent mail that was later determined to contain a pipe bomb.

Federal officials have not arrested anyone connected to the crime as of Wednesday evening.