Clashes have broken out after large crowds of pro-EU demonstrators rallied in Ukraine’s capital against new laws which aim to curb public protests.
Stun grenades and flares were thrown as groups of people headed for parliament, which was cordoned off by rows of police and buses.
Opposition politician Vitali Klitschko tried to stop attacks on police.
The laws were passed with a quick show of hands on Thursday by MPs loyal to President Viktor Yanukovych.
The opposition accused the ruling party of a coup.
US and EU officials have expressed deep concern at the new legislation.
Ukraine’s current anti-government movement began in protest at Mr Yanukovych’s decision in late November to pull out of a landmark treaty with the EU, but has expanded to demand his resignation.
Action plan demand
Sunday’s rally in Kiev heard calls from opposition politicians to disregard the new laws banning rallies that pro-EU protesters have been staging for the past two months.
Clashes erupted as some people headed away from the main square towards parliament, encountering cordons set up by police. Live TV pictures showed them attempting to overturn a bus used by police. The bus was set on fire after petrol bombs were thrown.
BBC Kiev correspondent David Stern said tensions had been rising and that the situation was very combustible.
Earlier the rally on the main square heard a call from a former Ukrainian navy chief for members of the armed forces to defy “illegal” orders from those in power, Unian news agency reported.
Rear Adm Ihor Tenyukh, who was sacked by President Yanukovych in 2010, warned of the dangers posed by the “coup d’etat planned by the current authorities”.
“Tomorrow the regime will enslave you too. Therefore we are calling on you to fulfil your military oath of loyalty to the Ukrainian people and not to the authorities who have gone off the rails,” he was quoted as saying.