The abductors of two National Hydel Power Corporation officials have demanded Rs 5 crore ransom for the safe release of each of the hostages.
The hostage-drama entered the fifth day on Tuesday.
Sources said the kidnappers contacted the families of NHPC General Manager (projects) T Mandal and Chief Engineer K Singh in Delhi to convey their demand.
"The calls have been tapped...the kidnappers want the payment immediately," an NHPC official said.
The police, meanwhile, raided several places in Patna, Muzaffarpur, Vaishali and East and West Champaran looking for the hostages.
Seven persons have so far been taken into custody for interrogation.