PORTLAND, Ore. (AP) — Protests in Portland, Oregon, were chaotic again even after the mayor pleaded with demonstrators to stay off the streets. Police arrested 12 people and say an officer was severely injured by a rock early Friday. Other demonstrators outside a police precinct used tire-puncturing devices to disable police vehicles. The clashes this week have ratcheted up tensions in the city days after an agreement was reached for federal agents to stop defending a federal courthouse that was the target of the protests. The nightly protests have taken place since the police killing of George Floyd in Minneapolis last May.