Five Ukrainian police were killed by friendly fire in a tragic accident in which officers mistook colleagues for burglars, officials said Sunday.
Three burglars initially escaped the crime scene amid a gunfight between different security forces, although they were later detained.
"Last night a devastating tragedy took place that killed five police officers," Anton Gerashchenko, a lawmaker and advisor to the interior ministry, wrote on Facebook.
The regional police force confirmed the incident, while President Petro Poroshenko wrote on Twitter that "the causes of this painful tragedy must be investigated and all the guilty must be punished."
The deadly mix-up came as special police staked out a "dangerous gang of burglars" in the small town of Knyazychy, some 30 kilometres (18 miles) east of Kiev, Gerashchenko said.
Two undercover police from the criminal investigation department were watching the scene as special police prepared to detain the gang.
"But a tragic series of chance events ruined the plan," Geraschenko said.
A burglar alarm went off in a house nearby, prompting the arrival of the State Guard Service -- a police force that protects property -- whose officers promptly detained the two undercover police.
The special police officers then mistakenly thought the burglars had captured their undercover colleagues and opened fire.
"Two State Guard Service officers, two undercover police and a KORD special police officer were killed," Gerashchenko said.
The gang of three burglars fled the scene but were detained as they travelled back to Kiev.
The Prosecutor-General's Office has launched an investigation.