Mobile phone footage showing the beatings that were carried out by prison warders (Video courtesy of Kenya's NTV)
Kenya's vice-president has condemned the alleged assault of prisoners by warders and ordered an investigation.
The incident, shown on Kenyan TV, was filmed secretly on a mobile phone and shows naked inmates at a Nairobi jail on the ground as warders beat them.
Kalonzo Musyuko said the footage would be studied and ordered the prisons commissioner to take action.
It is alleged one prisoner died of his wounds during an operation by warders to confiscate inmates' mobile phones.
Inmates in Kenyan prisons are not allowed to possess or use mobile phones.
Anybody who is concerned about human rights will be shocked about what was happening
Dickson Mwakazi Prisons department spokesman
Officials at the Kamiti Maximum Prison denied that the inmate's death was caused by the assault, saying he had been sick.
The BBC's Wairimu Gitahi in the capital, Nairobi, says in the video warders were seen armed with whips and batons, beating the inmates who were screaming uncontrollably.
The shocking footage was aired by two local TV stations and it is not clear whether it was filmed by an inmate or a concerned warder.
Mr Musyoka, who also heads the Home Affairs Ministry which oversees the prisons department, received a copy of the video from the state-funded Kenya National Commission on Human Rights (KNCHR).
Earlier this year a taskforce was set up to probe prison conditions
"We want to able to be a country that is able to observe everybody's human rights... So the excesses that were witnessed in Kamiti will certainly be dealt with," Mr Musyoka said.
A Kenyan prisons department spokesman said he was shocked by the video clip.
"Anybody who is concerned about human rights will be shocked about what was happening. When I saw it, I was also personally concerned [about] whatever was being done," prisons department spokesman Dickson Mwakazi told the BBC.
A KNCHR official, Njonjo Mue, who visited the prison, said 12 prisoners were injured during the assault.
Our reporter says the search operation was ordered following reports that prisoners were behind a scam in which mobile phone users were being conned out of money through bogus text messages.
Prison officials say more than 150 phones were seized during the search on Monday.
The prisoners later staged a strike to protest their fellow inmate's death.
Mr Mwakazi said investigations into the matter had been launched, but added that prison authorities were allowed to use force in some circumstances.
"Of course prison officers are allowed to use certain force to restrain whoever is trying to restrain either an inspection or enforcement of the law," he said.
In April, prison warders around the country staged a strike over their pay and allowances and threatened to release prisoners.
The government agreed to increase their allowances and set up a taskforce to probe conditions in the country's prisons.
The team recommended an overhaul of the service, and as a result, a new prisons commissioner and deputy were appointed.
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