A crude bomb exploded near a school in Raipur on Tuesday afternoon but no one was injured in the incident, police said.
Superintendent of Police of Raipur Deepanshu Kabra told PTI that the identity of the miscreants is yet to be ascertained.
The explosion broke the glass panels of the windows of the school, he added.
The police found a letter on the spot which said 'Don group has returned to fight injustice'.
Police said they have started investigations.
This is the third instance of an explosion of a crude bomb in the city. Last year, the members of the so called Don group had exploded a crude bomb at a cinema hall and later in a bus near the Bhartiya Janata Party office.
The police at that time had claimed that they had arrested three persons in connection with the incident.