Around 40 Maoists laced with firearms arrived at the spot and hurled two petrol bombs before torching an earthmover and a dumper this evening, officer-in-charge of Kathikund police station N S Dadel said.
A Deoghar-based construction company was constructing the bridge, he said.
Former Chief Minister Hemant Soren had laid the foundation of the bridge in February last year, bring constructed at a cost of Rs 4.15 crore.