We've just heard from Capitol Police Chief J Thomas Manger, who spoke to the press in Washington DC about an arrest made at the Capitol visitor centre.
He says that at about 12:20 local time (17:20 GMT) a white male entered the south entrance of the Capitol visitor centre.
When the man put his jacket and backpack through for screening officers saw what appeared to be "something in the shape of a firearm" and "two bottles in the backpack", he says.
As the man was standing there, one of the officers noticed a "faint odour of gasoline", he said. The smell was "much stronger" on the backpack and it appeared a bottle containing a substance - which police believe was either gasoline or "some other accelerant" - was leaking.
The man was then detained and arrested, Manger said. Police found a flare gun, a lighter and a torch lighter, he added, and there were also "other articles" in his backpack.
The man had "papers with him" and told officers his intent was to deliver them to Congress, Manger said. Police are still trying to determine "where in fact he did come from" and what his intentions were.
The investigation is "ongoing" and the man is in custody, Manger said.