Supporters of incumbent US President Donald Trump clashed with Antifa activists outside the Washington State Capitol building on Saturday.
The two groups met during two opposing events in Olympia, and this encounter resulted in violent brawls between the participants.
Videos emerged on social media, showing some of the activists using US flags as weapons during the clashes.
One of the videos apparently shows an activist pointing a handgun at Antifa protesters.
Another footage shows the man firing the weapon.
Later, police confirmed that an individual who "appeared to fire at least one round from a handgun into the opposing crowd" had been arrested.