A Kenyan death row inmate has been operated on to remove a cellphone from his large intestine, a prison warder said Wednesday.

Medical teams at a hospital in Naivasha town, northwest of the capital Nairobi, on Tuesday night extracted the device wrapped in a plastic bag from the gut of the prisoner after the device showed up on an X-ray.

"There was a mobile phone in the body and it's worrying the lengths these inmates can go to smuggle things into prison," prison chief Patrick Mwenda told reporters.

Mwenda did not specify how the inmate, identified as Bernard Kosgey, had introduced the phone into his intestine but said doctors established it had been wedged there for a month.

Earlier, tests with a metal detector had showed that Kosgey was carrying a metallic object but a body search conducted by warders produced nothing.