WASHINGTON, United States -- A man who threatened to set off a bomb on Washington's Capitol Hill surrendered to police Thursday, ending an hours-long standoff that rattled lawmakers still shaken by January's pro-Trump insurrection.

The incident triggered evacuations and a massive police response, and sent jolts of anxiety through a city that has spent months on alert, as political tensions soared following the deadly US Capitol riot.

The suspect, an apparent right-wing extremist identified by authorities as Floyd Ray Roseberry of North Carolina, was broadcasting live on social media from his truck, assailing President Joe Biden and Democrats, warning of a ''revolution,'' and complaining about the US government and its policy in Afghanistan.

He had also claimed that four more sets of explosives were lying in wait in Washington and that they would be detonated, along with his bomb, if police used deadly force against him.

Much of the complex was cordoned off as officers and FBI agents negotiated with the driver, who police said had appeared to have a detonator in his hand.

Suddenly, after four hours of drama, it was over.

''He got out of the vehicle and surrendered, and the tactical units that were close by took him into custody without incident,'' US Capitol Police Chief Thomas Manger told reporters.

A subsequent search by law enforcement found no bomb in the vehicle parked on the sidewalk next to the Library of Congress, ''but possible bomb making materials were collected from the truck,'' the USCP said in a statement.

Manger said it was unclear what Roseberry's motives were, but in his Facebook Live steam he issued a series of incoherent threats and asked to speak to the president.

''I'm trying to get Joe Biden on the phone. I'm parked up here on the sidewalk right beside all this pretty stuff,'' said the bald-headed man with a salt-and-pepper goatee, wearing a white T-shirt.

''I'm not hurting nobody Joe. I'm not pulling the trigger on this thing. I can't,'' he said. ''I'm telling you, them snipers come in, they start shooting this window out, this bomb's going off.''

'The revolution'

The live feed showed Roseberry in his vehicle holding a metal cylinder topped with clay attached to a box with buttons and wires, but it was ultimately determined not to be a viable explosive device.

While he did not claim a political affiliation, he referred at one point to ''the revolution'' and said: ''I'm looking for all my other patriots to come out and help me.''

Later he lashed out at Biden's party, saying: ''You all know what you're doing, Democrats? You're killing America.''

A White House official said Biden was briefed on the standoff.

As authorities revealed the threat, the Library of Congress's main buildings were evacuated, as was the nearby US Supreme Court and at least one of the three House office buildings.

Streets and buildings were re-opened and public transportation resumed after police gave the all clear.

'Threat to every community'

Both the Senate and House of Representatives are currently on recess, but some lawmakers have remained in Washington and staffers are working in the complex.

House Democrat Bill Pascrell offered fierce condemnation of the suspect during the standoff, in comments that echoed the trauma of the insurrection that rocked the Capitol in January.

''A right-wing extremist is now threatening to detonate a bomb at the US Capitol,'' he tweeted. ''Right wing domestic terrorism is a threat to every community in the United States.''

Tensions remain high more than seven months after the January 6 riot, when supporters of then-president Donald Trump stormed the US Capitol, fought with police and sought to block certification of the presidential election.

In April, a man rammed a car into Capitol barriers, killing one officer before the attacker was shot and killed.

Messages of appreciation poured in Thursday from lawmakers to the police officers assigned to keep the Capitol area secure.

''They have been through so much this year, and still they stand in defense of our democracy,'' Senator Martin Heinrich said.