Three policemen were injured when Maoists attacked their make-shift camp at Cone village in Latehar district of Jharkhand in the wee hours on Tuesday.
The ultras attacked the camp of the security men past midnight triggering an encounter which continued till 4 am, Superintendent of Police D B Sharma told reporters in Latehar.
Three policemen suffered injuries in the attack, while some Maoists were believed to have suffered bullet wounds in the encounter, he said.
More than thousand bullets were exchanged between the two sides, he said.
