St Louis’ top prosecutor has filed charges against a husband and wife who aimed guns at Black Lives Matters protesters marching past their house.

Mark and Patricia McCloskey, who are both personal injury lawyers in their 60s, have been charged with unlawful use of weapons after confronting the protesters outside their mansion in a gated St Louis estate in late June.

St Louis Circuit Attorney Kim Gardner told The Associated Press that the McCloskeys’ actions risked creating a violent situation during an otherwise non-violent protest.

“It is illegal to wave weapons in a threatening manner – that is unlawful in the city of St Louis,” Ms Gardner said.

A lawyer for the couple, Joel Schwartz, called the decision to charge them “disheartening”.

“I unequivocally believe no crime was committed,” he said.

Supporters of the McCloskeys said they were legally defending their $US1.15 million ($A2.14 million) home.

In interviews after the incident, Mr McClosky said he and his wife were “scared to death” by the protesters.

“This is all private property,” he told KMOV4 local news.

“There are no public sidewalks or public streets. I was terrified that we’d be murdered within seconds, our house would be burned down, our pets would be killed. We were all alone facing an angry mob.”

He told another local TV network he and his wife were confronted by an “absolute horde”.

Ms Gardner is recommending a diversion program such as community service rather than jail time if the McCloskeys are convicted. Typically, such felony offences can result in up to four years in prison.

Several Republican leaders have condemned Ms Gardner’s investigation, including President Donald Trump, Missouri Governor Mike Parson and Senator Josh Hawley, who has urged Attorney General William Barr to undertake a civil rights investigation of Ms Gardner.

In a radio interview last week, Mr Parson said he would likely pardon the couple if they were charged and convicted.

Ms Gardner said Mr Trump, Mr Parson and others are attacking her to distract from “their failed approach to the COVID-19 pandemic” and other issues.

St Louis, like many cities across US, was the scene of demonstrations in the weeks following George Floyd’s death at the hands of police in Minneapolis.

The McCloskeys’ home was initially incidental to the demonstration on June 28.

Several hundred people were marching to the nearby home of Democratic Mayor Lyda Krewson. She had angered activists by reading on Facebook Live the names and addresses of some who had called for defunding police.

A police report said the couple heard a loud commotion and saw a large group of people break an iron gate marked with “No Trespassing” and “Private Street” signs.

A protest leader, the Reverend Darryl Gray, said the gate was open and that protesters didn’t damage it.

Mr McCloskey confronted protesters with a semi-automatic rifle, screamed at them and pointed the weapon at them, according to a statement from police officer Curtis Burgdorf.

The statement said Ms McCloskey then emerged with a semi-automatic handgun, yelling at protesters to “go” and pointing the gun at them. Protesters feared “being injured due to Patricia McCloskey’s finger being on the trigger, coupled with her excited demeanour”, the statement said.

No shots were fired.

-with AAP