One national guard member has been killed and about 100 injured in violent protests outside Ukraine’s parliament, the interior ministry said.
Clashes between nationalists and riot police erupted after MPs gave initial backing to reforms for more autonomy in the rebel-held east.
National guardsmen were pelted with fire crackers and petrol bombs as explosions were heard.
The reforms are part of a peace plan to end fighting in eastern Ukraine.
Protesters led by the populist Radical Party and the ultra-nationalist Svoboda (Freedom) party – who fear the loss of the east to Russian-backed separatists – gathered outside parliament early on Monday.
After a rowdy debate, 265 MPs out of 450 backed the first reading of the decentralisation bill, granting more powers to areas of Donetsk and Luhansk.
Initially, there were only minor clashes but a BBC correspondent then heard small explosions followed by a much larger one – apparently from a grenade.
At the scene: Svyatoslav Khomenko, BBC News, Kiev
The demonstrators numbered barely more than a few dozen – mainly young men, most of them masked. They started the fights with police, but others supported them.
The protesters tried to pull the policemen away from their lines. They beat them and took their shields and helmets. Soon about a dozen young men were almost as well-equipped as the police.
Several times the atmosphere near the building seemed to calm down for a while, with clashes starting up again. And then the explosions began.
I saw some people – policemen and firemen – falling to the ground, and some running away from the site, limping. I saw pools of blood just near the wall of parliament.
The Ukrainian Interior Minister, Arsen Avakov, said some 30 people have been detained, including a Svoboda member who confessed to throwing a grenade.
He bitterly criticised Svoboda leader Oleh Tyahnybok, writing on Facebook that several explosive devices had been thrown by people wearing Svoboda T-shirts.
A policeman’s leg was torn off below the knee in the blast, Interfax Ukraine reported, while journalists at the scene were also reported injured.
Almost 7,000 people have died since the conflict in eastern Ukraine broke out in March 2014, after Russia’s annexation of the Ukrainian peninsula of Crimea.
Pushing through greater autonomy for the rebel-held areas is a key part of the Minsk peace deal, originally signed in February.
During the summer, fighting between Ukrainian army forces and the rebels has escalated. But the two sides agreed last week to halt the violence on 1 September, the day children in the region return to school.
Although the number of ceasefire violations appears to have fallen in recent days, OSCE monitors have warned that neither side was respecting the truce.
Under the draft constitutional changes going through parliament, there will be a special law covering local government in rebel-held areas.
However, parliament speaker Volodymyr Hroysman was adamant that would not mean special status for Donetsk and Luhansk, which rebel leaders have declared republics.
If President Petro Poroshenko is to succeed in pushing through the reforms, he will need the support of 300 MPs, seen as a tall order for the Ukrainian leader.
He is due to address the nation on the proposals and the violence outside parliament later on Monday.
Please include a contact number if you are willing to speak to a BBC journalist. You can also contact us in the following ways: