President Trump has stirred tensions before a gun rally in Virginia - a demonstration the state governor said carried credible "threats of violence" - by claiming that Americans' Second Amendment rights are "under attack".
Thousands of pro-gun activists are expected to march on Virginia's State Capitol on Monday to protest about the state's new gun controls.
The rally in Richmond has provoked fears of violence and unrest. Governor Ralph Northam declared a state of emergency this week, banning guns from the site of the rally, amid concerns that the protest will be flooded with extremists, anti-government militias and white supremacists. Activists in favour of gun control have reported receiving death threats online.
The FBI announced on Friday that it had arrested several members of The Base, a neo-Nazi group who were planning to attend, and seized their weapons.
Authorities said the group were planning violent acts at the rally, similar to the "Unite The Right" white supremacist rally in nearby Charlottesville in 2017, in which one counter-protester was murdered.
Mr Trump said on Friday that the US Constitution was being attacked by Virginia, where lawmakers have approved three gun control bills that could be passed next week.
The rules limit the purchase of handguns, stipulate new background checks, and permit local authorities to ban guns in public spaces. There are also plans by the Democrat-controlled legislative body to ban assault weapons.
Mr Trump said on Twitter: "Your 2nd Amendment is under very serious attack in the Great Commonwealth of Virginia", referring to the amendment in the Bill of Rights that gives Americans the right to bear firearms.
"That’s what happens when you vote for Democrats, they will take your guns away."
Shannon Watts, founder of the Moms Demand Action group that seeks tougher gun laws, said: "These extremists are afraid their guns will be taken away - we're afraid our children will be taken away."
Watts said that she and many members of her group and their families had been threatened online with death and rape. She said that members of her group in Virginia have had their addresses and other personal information shared online.
Philip Van Cleave, leader of the pro-gun Virginia Citizens Defense League (VCDL), the rally's organisers, has rejected calls for violence while encouraging militias from across the US to provide security for his group.