Activists of Thanthai Periyar Dravidar Kazhagam led by its general secretary, K Ramakrishnan, raised slogans against the Centre for giving a nod to Kerala for conducting an environmental impact assessment study for construction of a new dam at Mullaperiyar and attempted to show black flags, police said.
However, they were taken into custody and the flags were seized.
Ramakrishnan alleged that the Centre instead of solving the Mullaperiyar dam issue, was creating a "new problem" by giving a nod to the eco study.
Asked for his comments, Singh said, "In a democracy everybody has a right to demonstrate.