Ukrainian National Guard serviceman Ihor Debrin who suffered a lethal injury during clashes near the parliament on Monday was killed by a bullet rather than a grenade fragment, the Interior Ministry said.

"In fact, the main event was the explosions, and we now have information that the man who died was killed by a shot in his heart, by a bullet rather than by a [grenade] fragment," the Ukrainian interior minister's advisor Ivan Varchenko told Channel 5 on Tuesday morning.

"This is the latest information and I believe we will have a confirmation today," he said.

The police will question Svoboda leader Oleh Tyahnibok, Svoboda party member and parliament deputy Yuriy Syrotiuk and "other participants in that action," Varchenko said.

"I believe that very soon and, as I understand, this can quite possibly happen today, Tiahnybok, Syrotiuk and dozens of other people who organized and partnered those events will be summoned for questioning," the advisor said.

The presidential draft law introducing decentralization amendments to the Ukrainian constitution passed the first reading by 265 votes at the Verkhovna Rada on Monday.

Opponents of the bill clashed with the police near the parliament building. A conscript of the Ukrainian National Guard was killed in those clashes and the explosion of a grenade hurled at the police lines. More than 120 police officers and civilians, including media workers, were injured.

Ukrainian Interior Minister Arsen Avakov accused the all-Ukrainian union Svoboda and its leader Tiahnybok of the confrontations near the parliament. "The fact that Avakov 'named the culprits' so rapidly proves only that he was the one who planned that provocation," Tiahnybok said.