Several hundred protesters stormed a police station in southern Ukraine after authorities initially failed to arrest one of two policemen implicated in the rape of a young woman.
The outrage prompted Ukraine's President Viktor Yanukovych to order a top-level enquiry into the gang rape of 29-year-old Iryna Krashkova.
Residents of Vradiyivka in the southern Mykolayiv region hurled firebombs, bottles and stones as they attacked the police headquarters in the early hours of Tuesday.
Shots could be heard as police used tear gas against protesters, some of whom were covered in blood.
Locals also staged a two-hour rally in front of the police building later Tuesday.
According to the victim, who has a nine-year-old child, the two policemen raped her last week after taking her into the woods with the help of a taxi driver, who has also been detained.
Initially police detained only one officer leaving the other one free, saying he could not have been involved in the rape and claiming he was on duty that night.
But following the huge outcry, the local prosecutor's office announced on Tuesday that the second policeman identified by Krashkova, who remains hospitalised with a fractured skull after undergoing two operations, had been arrested.
Local resident Anatoly Burlak said the second policeman detained Tuesday was well known in the village for always being drunk and as a "sadist" who brutalised women.
It was widely thought that the policeman enjoyed the protection of local authorities because of family connections.
"If he comes out from prison alive he is unlikely to return to Vradiyivka," Burlak told AFP.
The region around Mykolayiv, a former shipbuilding hub and now a depressed southern city, has a grim reputation.
Last year, a teenage girl died after being set on fire and strangled in a gang rape by youths.
Burlak said two women, including a 15-year-old, had already died in the village after being brutally assaulted.
Interior Minister Vitaly Zakharchenko said Tuesday that the regional and village police chiefs had been sacked over the incident.
"Such shameful facts bring to nought all the positive police achievements," he told parliament in televised remarks.
The incident caused shock waves in the capital Kiev, with the president's office saying Yanukovych had asked the General Prosecutor to launch an investigation.
Ukraine's opposition said it would put together a special parliamentary commission to look into the crime and called for the dismissal of the interior minister.
"We believe that Ukraine cannot have an interior minister without control of a police force which torments, beats and rapes Ukrainians," said prominent opposition leader Arseniy Yatsenyuk.
The attack against the woman comes as the European Union is pushing Ukraine to stamp out corruption as the ex-Soviet country seeks to win an association accord with the bloc.
A seven-year jail term handed to opposition leader Yulia Tymoshenko on abuse of power charges in 2011 has severely harmed Ukraine's relations with the EU and is holding up the signing of the Association Agreement.