The officers were returning from Eku and Oria communities, where they had gone to quell boundary dispute when they ran into the attackers.
A source said the herdsmen used cattle to obstruct the vehicle of the policemen, and opened fire as the security personnel approached them to find out why the road was blocked.
An officer was said to have died on the spot, while another passed on, on the way to the hospital.
The other two died on Wednesday, at a hospital where they were receiving medical attention.
A policeman said the van which conveyed the policemen was riddled with bullets.
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Andrew Aniamaka, police public relations officer (PPRO) in the state, confirmed the attack, but said only one policeman died.
“Our men were attacked but only one inspector died in the incident,” he said.
“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.”
The attack happened about 24 hours after usman Ndanbabo, an assistant commissioner of police in the state, died after a gun attack.