Three suspicious packages have been found in the US, two addressed to a top Democrat and one to a former senior intelligence official, US media say.
Two items were found in a search of a Florida mail facility, and another at a Manhattan post office. Top Democrat Cory Booker and former national intelligence chief James Clapper were targeted.
The news came after several mail bombs were sent to prominent critics of US President Donald Trump.
The FBI has been searching the Florida facility for evidence. Ex-President Barack Obama and actor Robert de Niro were among those targeted.
Security camera footage at the postal facility in Opa-locka, Miami, is being scrutinised. A bomb squad and canine unit had accompanied federal officials to the site, police from Miami-Dade County said.
Meanwhile New York police described the Manhattan package as one that “closely resembled others sent across the country in recent days”. They said bomb squad personnel were on the scene.
Mr Clapper responded immediately to the news that he had been targeted, saying on CNN: “This is definitely domestic terrorism, no question in my mind. “There is some question about whether these things are functional or not – we probably have to assume they actually are,” he added, saying the incidents were not going to silence critics of the Trump administration.