Protesters and police clashed on Saturday morning in the western German city of Essen, the site of a two-day party congress by the far-right Alternative for Germany (AfD) that is due to get under way. Police made several arrests and said that some officers were attacked in violent incidents as thousands of demonstrators sought to blocade the venue and prevent AfD delegates from arriving. “Some demonstrators wore masks and attacked police officers,” Essen police said on Saturday. Authorities appealed to demonstrators to “keep away from violent actions and troublemakers.” Several hundred protest…