Three prisoners were shot dead in a clash at Ragauli district jail here on Friday, police said.
One of them died in an exchange of fire with jail officials after he shot dead the other two prisoners, jailor SP Tripathi said.
The deceased inmates have been identified as Anshu Dixit, Merazuddin alias Meraj Ali and Mukeem Kala, officials said in Lucknow.
"Dixit shot dead Ali and Kala, and held some of the other prisoners at gunpoint and threatened to kill them. He was later killed in the exchange of fire with police," IG, Chitrakoot Range, K Satyanarain said.
Asked how weapons reached inside the jail, the IG said, "The matter is being investigated."
He said all the three inmates were hardcore criminals and had a number of criminal cases pending against them.
However, Ragauli district jailor SP Tripathi earlier in the day said Dixit had snatched the service revolver of a jail staff when the official intervened in the argument between the inmates.