Nobody was injured in the blast that took place last night, they said.
"The IED was exploded to instill fear in the people so that the bandh can be clamped once again. But the people of Mirik were brave enough to defy the bandh and opened shops" senior TMC leader and minister Gautam Deb said.
The indefinite shutdown in the hills entered its 85th day today.
After nearly three months of shutdown, a large number of shops on Wednesday reopened in the Darjeeling hills, braving threats and intimidation by the Gorkha Janmukti Morcha (GJM).