The attackers had triggered at least 11 explosions and fired several rounds of gunshots, forcing authorities in the area to send a team of Special Auxiliary Police to the construction site, said director general of police Abhayanand.
Maoists blast bridge
Wednesday's assault, which came within weeks of a Maoist attack on the Mahabodhi temple complex in Bodh Gaya - one of Buddhism's holiest shrines, heightened concerns over a resurgence of Maoist violence and put the spotlight on the efficacy of the government's offensive against the rebels.
According to the police, more than a hundred Maoists took part in the attack in Goh, 180 km off Patna - Bihar's capital.
They had taken positions on the route that was expected to be taken by the SAP team and fired at them as they approached the base camp of the bridge construction site.
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Among the five dead, three belonged to SAP - an outfit of ex-soldiers from the Indian army and paramilitary forces who now work under the state police.
Two of the dead were private security guards. Among the seven wounded, the condition of two was serious.