Sources said the herdsmen used cattle to obstruct the police van to draw out the officers.
The assailants were said to have attacked a van the police officers were riding in.
The incident occurred on Tuesday, May 9, in Ethiope east local government area of the State.
It was gathered that the officers were returning from Eku and Oria communities, where they had gone to quell boundary dispute when they ran into their killers.
Sources said the herdsmen used cattle to obstruct the police van to draw out the policemen.
They allegedly opened fire as the officers approached them to find out why the road was blocked.
A media report said an officer died on the spot, while another gave up on the way to the hospital.
The other two died on Wednesday, May 10, at a hospital where they were receiving medical attention, the report said.
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The Police Public Relations Officer (PPRO) in the state, Andrew Aniamaka, however, said only one officer died in the attack.
He said, "Our men were attacked but only one inspector died in the incident.
"The remaining ones are in a hospital which I can’t disclose to the public for security reasons. They are recuperating.
"We are on the trail of the hoodlums behind this attack. As soon we are able to get them, they would tell us why they chose to lay ambush for our men."
About 24 hours before the attack, an assistant commissioner of police in the state, Usman Ndanbabo, had died after a gun attack.