Pro-West Ukrainians yesterday staged the biggest protest rally in Kiev since the 2004 Orange Revolution, demanding the government sign a key pact with the European Union and clashing with police.
Hundreds of protesters tried to storm the government building - after the main rally attracted tens of thousands in central Kiev - but police forced them back with batons and tear gas.
The opposition called the rally after President Viktor Yanukovych's government reversed a plan to sign a historic deal deepening ties with the European Union, in a U-turn critics said was forced by the Kremlin.
Police said that around 23,000 people turned out but the opposition said attendance met its target of 100,000 people. The centre of Kiev was covered in a sea of protesters waving EU and Ukrainian flags. The rally the biggest in Kiev since the Orange Revolution nine years ago, which resulted in the annulment of presidential election results initially claimed by Yanukovych.
A hard core of protesters proceeded after the rally to the government building and tried to break through the police ranks, with some throwing stones while police held them back.
Some opposition leaders attempted to calm down the protesters but demonstrators used the sticks from their protest signs against policemen and shouted "Revolution!"
Police held them back with batons and used tear gas and sound grenades. Another large group of protesters assembled near the building of the presidential administration and a smoke bomb was thrown, reports said.
But police did not make arrests or attempt to disband the rally, only standing guard at government building entrances.
Protesters earlier assembled at the central Square of Europe for a peaceful rally protesting the government's decision to scrap the signing of the landmark EU Association Agreement at a summit in Vilnius this week.
Some held posters saying "We are not the Soviet Union, we are the European Union" and "I Love EU". The crowd also chanted calls for unseating Yanukovych and releasing ex-premier Yulia Tymoshenko from jail.
The Kremlin, which wants Ukraine to join a Russia-led Customs Union, had threatened trade retaliation if Ukraine signed the deal. Yanukovych made a trip to Moscow earlier this month for secret talks with Russian President Vladimir Putin.
Tymoshenko, still a symbolic leader for the opposition, published a statement yesterday urging people to stay on central squares until the summit in five days and "force Yanukovych to change his humiliating decision and sign ... the agreement."
The rally demanded that Yanukovych disband his government, free Tymoshenko, and take the path to European integration.
"We feel that we are Europeans," said 19-year-old Alexandra Prisyazhnyuk. "We hope to show our force, to show that we mean something in our own country."
Rallies also took place in several Ukrainian cities. In the western city of Lviv the protest mustered an estimated 10,000 people.