Deadly clashes broke out between police and nationalist protesters in Kiev after Ukrainian politicians gave their support for greater autonomy in the separatist regions in the east.
At least two officers were killed and more than 140 people injured after grenades and firearms were used in some of the worst violence in the capital since the revolution that overthrew Viktor Yanukovych in February last year.
Igor Derbin, 25, was shot in the heart and Dmitry Slastikov died from injuries after a grenade explosion, the Interior Ministry said.
Both riot police and protesters used batons, tear gas and smoke bombs before a live hand grenade was thrown into a crowd outside the parliament building.
A video filmed from inside Parliament showed an object flying over the police cordon before an explosion that sent wounded officers scattering in several directions.
About 30 protesters were detained, including the man suspected of throwing the grenade.
Earlier in the day, Parliament passed the first reading of constitutional amendments that would decentralise some powers to regional governments. The amendments were passed by 39 votes in a fraught session. The changes are required under the Minsk peace agreement, a road map to ending the 16-month war with pro-Russian separatists in the east of the country.
The decentralisation plan is backed by Petro Poroshenko, the Ukrainian President, who is under intense pressure from Western governments to find a solution to the war that has claimed nearly 7000 lives. Supporters say the changes will allow Kiev to put pressure on the separatists and Vladimir Putin, the Russian President, to fulfil their part of the agreement, while critics say it is tantamount to surrender and legalisation of the occupation of large swathes of eastern territory.
The amendments will have to pass a much tougher second and third reading before being adopted.