"The encounter took place in Bakoria village, about 140 km from Ranchi in the wee hours. All the bodies have been recovered," Superintendent of Police Mayur Patel said.
Additional Director General of Police (Operation) S N Pradhan told PTI that the encounter took place around 1 am.
Getting intelligence inputs that the Maoists were moving in the district, the CoBRA battalion and the district police rushed to the spot.
On seeing the personnel, the Maoists got down from the vehicle and started firing on them, Pradhan said.
In the retaliatory action, 12 rebels were gunned down, he added.
The Maoists were moving in two vehicles. While one vehicle sped away, the naxalites from the other vehicle got down and opened fire on the police, Pradhan said.
It was the dasta (firing squad) of CPI (Maoist) 'zonal commander' RK alias doctor, the police officer said.
Eight weapons were recovered from the spot.
This is the first major incident in Jharkhand after Maoists had ambushed a police vehicle in Dumka on April 20 last year when the police party were returning after completion of the third phase of Lok Sabha elections.
Eight persons, including six policemen, were killed by the Maoists in that incident.