San Francisco braced for a weekend of protests, including a rally by an Oregon-based group that local leaders labelled white supremacist, as the city's mayor urged residents to boycott the event.

The demonstrations planned for Friday, Saturday and Sunday across the Bay Area raised concern among San Francisco police and elected officials two weeks after white supremacists, including neo-Nazis and Ku Klux Klan members, attacked anti-racism protesters in the streets of Charlottesville, Virginia.

A woman was killed at that "Unite the Right" rally when a man thought to have neo-Nazi sympathies drove his car into a crowd of counter-protesters. Nineteen other people were injured.

The Saturday event is billed as a "free speech" rally, but critics say the Oregon-based organisers, Patriot Prayer, is a white nationalist group, pointing to plans that may include the far-right Oath Keepers to provide armed security. The group has decried racism and neo-Nazis.

Far-right groups often use the guise of free speech to incite hatred.

Last weekend, 33 people were arrested in Boston as tens of thousands of demonstrators took to the streets to protest a free speech rally featuring far-right speakers.

'Preaching violence and hatred'

In San Francisco, city officials including Mayor Ed Lee had lobbied the National Park Service to deny Patriot Prayer a permit to hold a free-speech event at Crissy Field, which is under federal control as part of the Golden Gate National Recreation Area.

When that permit was granted on Wednesday, Lee told residents of San Francisco to essentially boycott the rally.

"I ask our public and our residents of the San Francisco Bay Area to honour our request to not dignify people who are coming in here under the guise of patriot and prayer words to really preach violence and hatred," Lee told a press conference.

The mayor urged locals to instead attend city-hosted events on Friday and Saturday that he said would focus on "inclusion, compassion and love rather than hate".

US House Democratic leader Nancy Pelosi, in a written statement, slammed the Patriot Prayer gathering as a dangerous "white supremacist rally."

READ MORE: UN issues rare warning over 'alarming' racism in US

Left-wing counter-protesters, meanwhile, were planning a march to Crissy Field, where police were concerned that a confrontation could erupt between the two groups.

Patriot Prayer founder Joey Gibson said in a video message posted on the group's Facebook page that it was "absolutely not" white supremacist, pointing out that he is a person of colour.

"What I'm trying to do is bring people together who believe in freedom, who believe in love, believe in peace and believe in free speech," Gibson said.

But the Southern Poverty Law Center (SPLC), an organisation that monitors hate groups, has said Patriot Prayer rallies in the past have been "designed to provoke violence and [are] populated with extremists".

'Adopt a Nazi'

The Jewish Bar Association of San Francisco has launched a campaign titled, "Adopt-a-Nazi (not really)" to counter the narrative of Saturday's protest.

READ MORE: 'Adopt a Nazi': How groups are countering neo-Nazis

Individuals are asked to donate money for every person who plans to attend the Patriot Prayer rally in an effort to help white supremacists and neo-Nazis "fund their own demise".

So far, the group has raised more than $139,000 for the SPLC.

On Sunday, conservative activists planned a so-called "No to Marxism" rally in nearby Berkeley, an event that left-wing groups were also expected to protest. However, City of Berkeley officials on Thursday denied that group's request for a rally permit, putting the event in jeopardy.

In April, supporters and opponents of US President Donald Trump clashed in a Berkeley park, resulting in at least 20 arrests as well as bloodied faces and minor injuries.