About a hundred policemen were wounded in protests outside Ukraine’s parliament building on Monday as lawmakers approved on first reading amendments to the constitution that will give greater autonomy to the eastern regions controlled by Russian-backed rebels, newswires reported.

A loud explosion was heard when an unknown individual threw a grenade into police ranks, according to Ukriane’s unian.info. The blast caused severe injuries.

Over 3,000 people opposed to the amendments that give more powers to the authorities of Donetsk and Luhansk regions set up pickets outside the parliament building in Kiev at the time when the MPs were giving their approval to the controversial decentralization legislation that is a part of the Minsk peace accords signed between Ukraine’s government and pro-Russian rebels in February.

Police have detained 30 protesters during the rally including the grenade thrower, Ukraine’s Interior Minister Arsen Avakov has said.