Many law enforcement agencies received reports on Wednesday of two suspected devices, one each at the headquarters of the Republican National Committee and the Democratic National Committee, the FBI said in a statement on Twitter.

Thursday’s statement was accompanied by an image of a masked suspect wearing gloves and a hoodie, carrying an object.

“The FBI is offering a reward of up to US$50,000 for information leading to the location, arrest and conviction,” the agency’s Washington field office added.

Wednesday’s breach of the US Capitol by supporters of US President Donald Trump was a stunning assault on American democracy when lawmakers were certifying the victory of president-elect Joe Biden.

Trump condemned the violence after having initially praised his supporters. He added that the rioters had defiled the seat of American democracy and must be held accountable.

Senators and Congressmen were forced to evacuate after hundreds of Trump supporters stormed the legislative building, smashing windows and engaging in looting.

The violence, which killed five people, followed a rally at which Trump exhorted supporters to “fight” to overturn the Nov 3 election.