BEIJING (AP) — Beijing police say they have detained 67 people involved in a suspected pyramid scheme after its members held a rare, large-scale demonstration in the capital this week to protest the government's investigation.

Videos circulating on social media purportedly showed hundreds of people waving Chinese flags and banners on Monday to demand that authorities back off the investigation of the Shenzhen-based "Kindness Exchange" investment fund. The members have defended it as a legitimate poverty relief charity.

Police said on social media late Wednesday that the protest this week was an "illegal gathering" incited by group members.

Chinese authorities have struggled to contain the proliferation of Ponzi schemes that have used social media to recruit elderly or less-educated members.