Union Home Minister P. Chidambaram has written a letter to West Bengal Chief Minister Buddhadeb Bhattacharjee expressing serious concern at the law and order situation in West Bengal. The Home Minister asked the State Government to ensure that the armed cadres belonging to 'Harmad Vahini' are immediately disarmed and demobilised. He said it was a matter of grave concern that these cadres have been provided with arms. Mr. Chidambaram said the violence presented an alarming picture which was completely unacceptable in a democratic system. Chidambaram's letter comes in the wake of Trinamool Congress alleging misuse of Central Security forces in the State.