Fighting has resumed at Afghanistan's main prison, parts of which have been taken over by rioting detainees.
Reinforcements have been sent to the high-security prison
Security forces fired at inmates at Kabul's Pul-e-Charkhi jail, where hundreds of rioters, including Taleban and al-Qaeda militants, are barricaded.
Tuesday's unrest followed an apparent breakthrough on Monday - when officials agreed to distribute food and water to the protesters, and restore power.
The riot began on Saturday with inmates demanding better conditions.
Security forces are surrounding the area and an unmanned drone aircraft is circling overhead.
Officials say they are seeking a peaceful solution to the stand-off, but have pledged to use force if talks fail.
Late on Monday negotiators reached a deal with the rioters. Besides receiving food and water, the inmates handed over the bodies of four of their group who had been killed in the initial riots.
Several injured prisoners were also taken to hospital.
However on Tuesday officials said the rioters had backed away from the agreement.
Security forces told the BBC's Bilal Sarwary outside the prison that prisoners were fired upon after several tried to break out.
Troop reinforcements were sent, and a group of about 50 security officers was seen heading towards the jail.
Mediator Mawli Sidiq - a member of the Afghanistan Ulema Council, a religious body - told our correspondent negotiations should be given another chance.
Inmates are reported to be armed with knives and makeshift clubs, but not guns.
Trouble started on Saturday evening, apparently sparked by a change in prison uniform rules.
Pul-e-Charkhi is a huge prison complex built in the 1970s on the outskirts of the capital.
Correspondents say the vast and run-down jail is notorious for the disappearance and torture of thousands of Afghans during the communist era.
Last month, seven Taleban suspects escaped from the jail, with prison guards accused by officials of helping the break-out.
Following the escape, prison authorities ordered inmates to wear bright orange uniforms.