Seeking to prevent a pair of right-wing weekend rallies from spiralling into violence, Bay Area authorities are vowing a bolstered police presence and urging counter-protestors to stay away as federal officials rebuffed a high-profile attempt to halt a San Francisco rally.

While organisers of the events in Berkeley and San Francisco have disavowed racism and violence, elected officials and police officers are on high alert after a car rammed into a a crowd of counter-protesters against a white supremacist march in Charlottesville, Virginia two weekends ago.

Anger over the bloodshed, combined with the Bay Area’s propensity for intense activism and a history of clashes at protests, makes for a volatile mix. Ahead of a scheduled “No Marxism in America”, rally in Berkeley, posters announcing “Nazis are coming” have appeared around town, a message promoted by the Berkeley branch of an anti-fascist group - called Antifa for short - that has battled with white supremacists in the past.

Politicians in both cities lambasted what they called forces of division and bigotry but asked citizens not to give rally organisers the reaction they crave.

An effort by elected officials to block the "Patriot Prayer" event at San Francisco's Golden Gate National Recreation Area failed as the National Park Service said the event would be allowed to proceed, overriding a request from Rep. Nancy Pelosi, D-California, Mayor Ed Lee and Sen. Dianne Feinstein, D-Calif., to revoke a permit. After considering the request, the park service announced on Wednesday that the event would be allowed to proceed, saying it could not deny a permit based on based on a “political stance or beliefs”.

In response, Ms. Pelosi released statement ruing the “ill-conceived decision” and said “we must all pray it does not become an invitation to incite violence”. Soon after the park service announced its decision, Lee convened a press conference at San Francisco City Hall in which he pronounced himself “deeply disappointed” and urged citizens to ignore rightwing agitators.

“I ask that people avoid going to Crissy Field and engaging with members of Patriot Prayer, because that is precisely what they wish us to do”, Mr. Lee said. “And I don't want to dignify their message of hate and their message of division”.

As he spoke Mr Lee was flanked by San Francisco Police Chief Bill Scott, who stressed that guns and ammunition would not be allowed at the event and said that police officers would not escort attendees. He reiterated that the department would marshal a surge in officers.

"You will see a very, very large presence of officers", Mr Scott said, adding that "we are staffing up for that".

Violence on the streets of Charlottesville Show all 9 1 /9 Violence on the streets of Charlottesville Violence on the streets of Charlottesville Protesters clash and several are injured White nationalist demonstrators clash with counter demonstrators at the entrance to Lee Park in Charlottesville, Virginia. A state of emergency is declared, August 12 2017 Violence on the streets of Charlottesville Trump supporters at the protest A white nationalist demonstrator walks into Lee Park in Charlottesville, Va., Saturday, Aug. 12, 2017. Hundreds of people chanted, threw punches, hurled water bottles and unleashed chemical sprays on each other Saturday after violence erupted at a white nationalist rally in Virginia. AP Photo Violence on the streets of Charlottesville State police stand ready in riot gear Virginia State Police cordon off an area around the site where a car ran into a group of protesters after a white nationalist rally in Charlottesville, Virginia AP Photo Violence on the streets of Charlottesville Militia armed with assault rifles White nationalists, neo-Nazis and members of the 'alt-right' with body armor and combat weapons evacuate comrades who were pepper sprayed after the 'Unite the Right' rally was declared a unlawful gathering by Virginia State Police. Militia members marched through the city earlier in the day, armed with assault rifles. Getty Images Violence on the streets of Charlottesville Statue of Confederate General Robert E Lee The statue of Confederate General Robert E. Lee stands behind a crowd of hundreds of white nationalists, neo-Nazis and members of the 'alt-right' during the 'Unite the Right' rally 12 August 2017 in Charlottesville, Virginia. They are protesting the removal of the statue from Emancipation Park in the city. Getty Images Violence on the streets of Charlottesville Racial tensions sparked the violence White nationalists, neo-Nazis and members of the 'alt-right' exchange insults with counter-protesters as they attempt to guard the entrance to Lee Park during the 'Unite the Right' rally Getty Violence on the streets of Charlottesville A car plows through protesters A vehicle drives into a group of protesters demonstrating against a white nationalist rally in Charlottesville, Virginia. The incident resulted in multiple injuries, some life-threatening, and one death. AP Photo Violence on the streets of Charlottesville Rescue personnel help injured people after a car ran into a large group of protesters after an white nationalist rally in Charlottesville, Virginia AP Photo Violence on the streets of Charlottesville President Donald Trump speaks about the ongoing situation in Charlottesville, Virginia from his golf club in Bedminster, New Jersey. He spoke about "loyalty" and "healing wounds" left by decades of racism.

In imploring his citizens to make other plans, Mr Lee echoed a Tuesday press conference on the steps of Berkeley City Hall in which a passel of elected officials denounced violence and issued a simple plea to counterprotesters: sit this one out.

Berkeley Mayor Jesse Arreguin acknowledged “we’ve seen hate groups and their sympathizers agitate on our streets” spouting “hateful rhetoric”, adding that “sometimes these people come eager for a fight”.

Yet “as much as you would like to show your physical opposition to hate, confrontations only serve the perpetrators”, Arreguin said, imploring citizens not to attend “for their own safety” and continuing to promote alternative events scheduled for that day.

Arrests at Antonio Martin demo in Berkeley

Similarly, Rep. Barbara Lee, D-Calif, warned that Donald Trump's remarks comparing white supremacists to leftist protestors “have emboldened white supremacists, white nationalists and neo-Nazis across the country” and called the planned demonstration “offensive” but said “let us be peaceful” in response.

“If no one shows up to their events, then they have no one to incite violence against. So those of us who don't want to see the violence, we will ignore them”, said Democratic state Sen. Nancy Skinner. “Do not come here...do not bite their bait and give them any circumstances. If they must do violence then they can do it against themselves.”

Berkeley city council members prepared for the unpermitted rally by passing a new ordinance expanding the areas in which police officers can confiscate weapons and take other measures to keep the peace to areas like sidewalks outside of public parks.