The Centre on Tuesday sent in about 400 troops of the paramilitary Border Security Force or BSF to West Bengal after a request from the state government trying to control Communal trouble near Kolkata. tension flared in several places in **rth 24 Parganas district over an offensive Facebook post on Friday about Prophet Mohammed by a 17-year-old student. The student has been arrested, but there have been violent protests in his town Baduria, about 70 km from Kolkata, and other areas nearby.