Only a few days after the alleged rape of a young woman by teenagers in Muelheim, Germany, another sexual assault case involving teens has emerged in the same city.

In the latest incident, a 15-year-old girl was allegedly surrounded by five boys aged between 11 and 17, and subsequently harassed and touched inappropriately on Monday evening, prosecutors in nearby Duisburg said the following day.

Prosecutors are now investigating four of the teenage boys, while the 11-year-old is not deemed criminally responsible under German law, which only allows children aged above 14 to be prosecuted.

The case comes amid shock over a gang rape that involved suspects as young as 12, also in Muelheim, which is located in the western state of North Rhine Westphalia.

Three 14-year-olds and two 12-year-olds are the main suspects in that case. One 14-year-old was arrested late Monday amid concerns he could be a danger to the public.

The head of Germany's GdP police union, Rainer Wendt, called for the age of criminal responsibility to be reduced to 12 years in light of this particular case.

But earlier on Tuesday, the German Judges' Association spoke out against a reduction in the age of criminal responsibility in Germany.

Juvenile justice has proven itself in principle, the association's chairman, Jens Gnisa, told dpa. "It has led to a significant decline in juvenile delinquency through the educational mission laid down within it," Gnisa said.

The German Child Protection Association also opposes such a step. The youth welfare office should instead respond and look at the causes of the child's behaviour in individual cases, the deputy managing director, Martina Huxoll-von Ahn, told dpa on request.

However, a spokesman for the city of Muelheim said that in the gang-rape case, the families of the suspects had rejected the help of the youth welfare office.