Dhaka, Nov. 30 -- Thousands of protesters rallied in the western German city of Giessen on Saturday as the far-right Alternative for Germany prepared to launch its new youth organization. Some demonstrators clashed with police, who used pepper spray and later water cannons to disperse blockades. Police said stones were thrown at officers at one site, prompting the use of pepper spray. In another area, around 2,000 protesters refused to clear a road, leading authorities to deploy water cannons.

The founding convention of the new AfD youth wing, expected to be named Generation Germany, was scheduled to take place at the Giessen convention center but had not begun two hours after its planned start. The group replaces the Young Alternative, an...