More than 100 people were detained overnight in Berlin amid clashes between bottle-throwing youths and police ahead of May Day rallies, police reported Saturday. A spokesman for the city said that 111 people were briefly held and some 60 police officers were lightly injured in the scuffles. In what has become an annual ritual with no obvious political links, Berlin youths broke up a pacifist May Day assembly in Mauerpark in the city's eastern part and began hurling beer bottles and other projectiles at police who attempted to restrain them. Further protests are expected later Saturday in Berlin's multi-ethnic Kreuzberg district, where the clashes with police are usually heaviest. In order to maintain order in the city during the labor day rallies, some 8,000 police have been mobilized. Authorities have also warned that those resorting to violence could face up to 10 years in jail. The U.S. state department has issued a special warning to Americans to exercise caution in certain parts of Berlin over the May Day weekend. "In recent years anarchists, skinheads and extremists have congregated in Berlin on May 1, where they have set cars on fire, broken shop windows, and fought with police, resulting in numerous injuries," it stated.