Berkut is an elite riot police force that has been at the forefront of recent deadly clashes there.
Its members have now been accused of beating, torturing and even shooting demonstrators.
Unprovoked attacks on journalists and medical workers have also been alleged.
Most recently, a video clip emerged, showing a naked protester apparently being abused and beaten by riot policemen who had stripped him in below-freezing temperatures.
While food and hot drinks were offered by sympathetic demonstrators to police officers and army servicemen amid the stand-off in late 2013, Berkut members have borne the brunt of anti-government ire after tensions flared up in January.
What is Berkut?
Berkut members are reported to be more carefully selected, better trained, paid and equipped than ordinary police units.
They are also said to have more senior officials as commanders.
The force was set up in 1992 and has its roots in Omon, the notoriously ruthless Soviet "special-purpose police".
Initially, Berkut's primary goal was to fight organised crime, but it has now changed to ensuring law and order during "mass events".
The Interior Ministry itself is headed by Vitaliy Zakharchenko, a steadfast supporter of President Viktor Yanukovych.
Mr Zakharchenko hails from the president's home region of Donetsk and is also reported to be close to his son, Oleksandr.
The media in Ukraine describe Berkut as an elite riot police force, whose members are carefully selected and rigorously trained.
To be accepted into Berkut, army service and at least two to three years of law-enforcement experience are said to be compulsory.
Chances of employment with Berkut increase if the applicant is an athlete with a proven track record, the media report.
Berkut has about 4,000 to 5,000 members stationed across Ukraine.
Local units are directly subordinated to the heads of regional Interior Ministry departments, instead of lower-ranking police officials such as district police chiefs.
It is not unusual for Berkut units to be dispatched from their bases to other regions.
Report say that many of them have been brought to Kiev from eastern Ukraine, which is more supportive of President Yanukovych.
Berkut members from more opposition-minded western Ukraine, meanwhile, have complained to the media that they were "mistrusted" by top commanders.
Berkut has some serious hardware at its disposal, including machine guns and armed personnel carriers.
Its members are also reportedly paid 1.5-2 times more than an average police officer.
Source: BBC News