Suspected explosive devices were sent to former Secretary of State Hillary Clinton and former US President Barack Obama, the US Secret Service has said.
It comes two days after a bomb was found at the home of liberal philanthropist and financier George Soros in the suburbs of New York City.
The devices were discovered by technicians who screen mail sent to the former US officials.
The Time Warner building in New York was also evacuated due to a package.
CNN, which is located in the Time Warner building, reported that it evacuated its newsroom over a suspicious package.
According to a statement from the US Secret Service, the first package was addressed to Mrs Clinton and was recovered late on 23 October.
"Early this morning, October 24, 2018, a second package addressed to the residence of Former President Barack Obama was intercepted by Secret Service personnel in Washington, DC," the statement adds.
"Both packages were intercepted prior to being delivered to their intended location. The protectees did not receive the packages nor were they at risk of receiving them."
A US official told the Associated Press that a "functional explosive device" was found during a screening of mail sent to the home of Mr and Mrs Clinton in Chappaqua, New York.
The FBI in New York said they were aware of the suspected packages, and are aiding in the investigation.
A spokeswoman for Mr Obama declined to comment on the incident, and referred reporters to the Secret Service statement.
The suspected explosive devices come two days after a confirmed pipe bomb was discovered in a mailbox at the home of Mr Soros.
Mr Soros has become a frequent target for criticism by right-wing groups due to his support for liberal causes.
Officials "proactively detonated" the device, and determined that it contained explosive powder and "had the components of a bomb".
White House spokeswoman Sarah Sanders condemned the "attempted violent attacks" against the public figures.
"These terrorising acts are despicable, and anyone responsible will be held accountable to the fullest extent of the law.
"The United States Secret Service and other law enforcement agencies are investigating and will take all appropriate actions to protect anyone threatened by these cowards," she said.
The US President's eldest son, Donald Trump Jr, who received suspicious packages at his New York home earlier this year, tweeted: "As someone whose family has directly been the victim of these mail threats I condemn whoever did this regardless of party or ideology.
"This crap has to stop and I hope they end up in jail for a long time."
Source: https://www.bbc.co.uk/news/world-us-canada-45969100
UPDATE: A man has been arrested in connection with the mail bombs.
https://www.bbc.co.uk/news/world-us-canada-45996655
