Lawyers for Donald Trump have responded to his impeachment charges, saying supporters of the former US president stormed Congress in Washington DC on 6 January of their own accord.

Mr Trump's trial in the Senate is due to begin on Tuesday after he was impeached for the second time by the House of Representatives last month.

He is charged with "inciting insurrection" in a speech to supporters ahead of the deadly riot.

Mr Trump says he will not testify.

Five people, including a police officer, died when a mob of Trump supporters attacked the Capitol building, forcing politicians and staff to hide in offices.

Mr Trump is the only US president in history to have been impeached twice and one of only three to have been impeached at all.

In a pre-trial brief released on Monday, the former president's lawyers said that FBI documents had shown that the riot was planned days in advance, meaning that Mr Trump cannot have encouraged the violence.

They also insist the trial is unconstitutional because Mr Trump has left office and is now a private citizen.