Nancy Pelosi's husband Paul recovering after hammer attack surgery

The suspect, David Depape, 42, is said to have demanded to see Mrs Pelosi.

President Biden described the attack as "despicable" and denounced a corrosive political climate for contributing to violence.

"Enough is enough is enough," he said during a speech in Philadelphia. "Every person of good conscience needs to clearly and unambiguously stand up against the violence in our politics, regardless of what your politics are."

Hours after the attack, the US government distributed a bulletin to law enforcement across the nation warning of a "heightened threat" of domestic violent extremism against candidates and election workers driven by individuals with "ideological grievances".

However, police investigating the attack on Mr Pelosi - which they have deemed an attempted murder - told reporters a motive had not yet been fully determined.

'Paul Pelosi made secret 911 call'

Mrs Pelosi - who was on the other side of the country in Washington DC at the time of the assault - flew back to see her husband in hospital.

A spokesman for the senior Democrat said Mr Pelosi had been attacked in the early hours of Friday morning "by an assailant who acted with force, and threatened his life while demanding to see the Speaker".

San Francisco Police Chief William Scott said officers had responded to a call at around 02:27 local time (09:27 GMT) on Friday.

They found Mr Pelosi and the suspect struggling over a hammer, but it was wrested from Mr Pelosi by the intruder, who violently assaulted him with it.

The suspect was tackled and disarmed by officers. He had attempted to tie up Mr Pelosi "until Nancy got home", law enforcement sources told CBS News. He reportedly shouted "where's Nancy?" during the incident.

He is also facing charges of assault with a deadly weapon, burglary and several other felonies, Chief Scott said.

He said the suspect had gained access through a rear entry to the four-bedroom Pelosi home in the upmarket neighbourhood of Pacific Heights. Footage shows a smashed glass door at the property.

The suspect is currently in hospital, but police declined to share details about his medical condition.

At the start of the break-in, Mr Pelosi told the intruder he needed to use the bathroom then made a secret 911 call on his mobile phone and left the line open, allowing a dispatcher to hear him talking to the suspect, reports the Los Angeles Times.

Chief Scott confirmed it was Mr Pelosi who had called police and that a quick-thinking emergency dispatcher had been "able to read between the lines" and send officers.

"This was not a random act," said the police chief of the attack. "This was intentional."

He added: "Everybody should be disgusted by what happened this morning."

Far right web activity

A blog, website and social media accounts under the name of the suspect seen by the BBC are filled with anti-Semitic memes, Holocaust denial, references to far-right websites and conspiracy theories such as QAnon.

He also posted debunked allegations of election fraud. His recent posts were rambling and touched on a host of far-right and extremist talking points.

Older messages by the suspect promote hemp jewellery and quartz crystals. He was also a nudist activist who had listed himself as a member of the Green Party, according to the San Francisco Chronicle.

The suspect grew up in the western Canadian province of British Columbia before moving to the US and becoming estranged from family members back home, his stepfather told the Globe and Mail newspaper.