US Capitol on lockdown after 'bomb threat' with possible 'explosive truck'

The US Capitol was placed into a lockdown after a "possible explosive truck" was found near the Library of Congress.

Capitol Police responded to reports of an explosive device in a vehicle close to the Washington building this afternoon.

Negotiators spoke to a man in the truck was said to be making threats, CNN reports.

The suspect was reportedly holding something in his hand, according to ABC.

Capitol Police said a bomb was not found in the vehicle, but possible bomb making materials were collected from the truck.

They added that the driver - 49-year-old Floyd Ray Roseberry - was in police custody.

Congressional staff members and journalists had been told to shelter inside their offices

The Supreme Court was evacuated, alongside the Cannon House Office and Jefferson buildings.

The US Capitol is on lockdown (AFP via Getty Images)

"The USCP is responding to a suspicious vehicle near the Library of Congress. Please stay away from this area and follow this account for the latest information," the police force tweeted at around 2.45pm GMT.

Around 15.30pm GMT they added: "This is an active bomb threat investigation. The staging area for journalists covering this situation is at Constitution and First Street, NW for your safety.

"Please continue to avoid the area around the Library of Congress."

US Capitol police block a street during the investigation into a possible bomb threat (AFP via Getty Images)

The FBI said in a statement that its Washington office's National Capital Response Squad was responding to the incident.

The Bureau of Alcohol, Tobacco, Firearms and Explosives released a statement on Twitter that they were also responding.

The vehicle is said to have no license plates.

The Republican National Committee building, which is nearby, was also evacuated, the Washington Post reports.

The identity of the driver has not been made public (AFP via Getty Images)

Construction workers at the Capitol were also told to move away from their site while police are asking people to "stay away from this area" while the investigation is ongoing.

Earlier this year a pipe bomb was left at the headquarters of the Democratic National Committee and the Republican National Committee in Washington.

A day later thousands of pro-Trump rioters stormed the U.S. Capitol on January 6.