NEW : 188 people have been arrested or detained , military police say . Comment: The violence involving drug gangs started with a transfer of prisoners , an official says . Two rival drug gangs collaborated to launch the attacks , the official says .
NEW : 188 people have been arrested or detained , military police say . Some Rio de Janeiro schools are closed as police focus on the main drug-dealing area . The violence involving drug gangs started with a transfer of prisoners , an official says . Two rival drug gangs collaborated to launch the attacks , the official says .