Twenty police officers sustained injuries as protesters attempted to take over the Chernihiv region administration building on January 25.

Some of them sought medical aid.

A spokesman for the Chernihiv region branch of Ukraine's Interior Ministry said on Thursday that four officers were being treated at hospitals, and another two were receiving outpatient treatment.

Two of the policemen sustained intracranial injuries and a concussion and another two suffered acoustic trauma during the January 25 clashes, he said.

"Most of the injured policemen sustained injuries to the head, limbs and back, as well as chemical burns to the eyes by an unknown gas. The Chernihiv region's deputy police chiefs were injured as well," the spokesman said.

A criminal investigation has been opened into the January 25 unrest, attempts to seize administrative buildings and attacks on officers of law enforcement agencies.