(CNN) Police in tense downtown Portland on Saturday ordered protesters to disperse and leave a location where they saw people throwing projectiles, including rocks and bottles.

"Failure to comply with this order may subject you to arrest or citation, and may subject you to the use of riot control agents or impact weapons," police said on Twitter and on a loudspeaker at the scene.

This came as dueling political rallies took place and police braced for potential violence. They told people not to bring weapons and warned that checkpoints and bomb-sniffing dogs would be on hand.

Members of law enforcement -- who wore heavy armor on the streets -- ran toward protesters and continued to move them farther away from the location where flash-bang grenades were deployed, a CNN affiliate live signal from the ground shows.

"We aren't here to fight the police," a protester yelled. "We're here to fight the Trump supporters."