At least four people have died after police moved to quell unrest in several jails in Kyrgyzstan, officials said.
Moldovanovka prison is at the eye of the storm
The violence was sparked by the authorities' removal of several inmates from Moldovanovka jail to another one, the deputy justice minister said.
Guards were withdrawn from Moldovanovka last month after an MP and three others were shot dead during a visit.
They had been investigating protests - over poor living conditions - which had also hit other jails in Kyrgyzstan.
On Tuesday, police killed two prisoners at Moldovanovka prison and another two at a jail in the village of Petrovka, also near Bishkek, Deputy Justice Minister Sergei Zubov told the Associated Press.
Kyrgyz media quoted other officials as saying more than 20 prisoners were killed, but the head of the country's national sentencing board, Kapar Mukeyev, dismissed reports of a higher death toll as "the product of fantasies of relatives of the prisoners and a few human rights activists".
Mr Zubov said there was rioting in practically all the country's jails after police arrived at Moldovanovka on Tuesday morning to remove 28 inmates suspected of involvement in the killing of MP Tynychbek Akmatbayev, two deputies and prison system director Ikmatullo Polotov.
1 November: Several jails hit by unrest after authorities move high-profile inmate
20 October: MP Tynchbek Akmatbayev and two aides shot dead during prison visit
22 September: MP and businessman Bayaman Erkinbayev shot dead
13 June: Security guards open fire on protesters in Osh, injuring at least seven
10 June: MP Jyrgalbek Surabaldiyev shot dead in Bishkek
1 June: Hundreds eject protesters from Supreme Court which they had held for more than a month
Special forces troops and armoured personnel carriers restored order in Moldovanovka, and seized grenades, submachine guns, rifles and pistols, a prisons service official, who refused to be named, told Reuters news agency.
"The situation is under our control at the moment," he said.
"It was an operation sanctioned by the prosecutor general to isolate several negatively behaving convicts and stabilise the situation in the prison," he added.
The most high-profile prisoner to be moved on Tuesday was criminal boss Aziz Batukayev.
"They [soldiers] beat him in front of the jail - apparently to intimidate other inmates - and took him to a SNB [security service] prison in Bishkek," Batukayev's sister Yakha told Reuters news agency.
A resident in the area said gunfire at Moldovanovka lasted about 30 minutes.
Moldovanovka was the scene of an MP's killing last month
Moldovanovka prison was also the scene of bloodshed last month, when MP Tynychbek Akmatbayev visited to investigate unrest over poor living conditions.
Akmatbayev and three others were subsequently killed by the inmates.
Prison guards were pulled out of Moldovanovka and other jails in Kyrgyzstan as a result. Prison officials returned to some of the prisons, but Moldovanovka and several others have been in the control of inmates since, Reuters said.
It is not clear why Akmatbayev was killed. Some analysts believe his death may have been linked to mafia rivalries in Kyrgyzstan.
His brother, Rysbek Akmatbayev, faces charges of ordering a mafia-related murder. He has led calls for Kyrgyz Prime Minister Felix Kulov to step down as a result of his brother's death.
Mr Kulov was imprisoned on political charges under the country's previous regime in Moldovanovka prison, and Rysbek Akmatbayev claims his brother was shot dead by a man who was an associate of Mr Kulov's when he was in prison.
Kyrgyzstan has witnessed several violent incidents since the overthrow of ex-President Askar Akayev in March.
Two other MPs have been killed in recent months.