Ukrainian opposition leaders yesterday called on President Viktor Yanukovich and his government to resign at a rally of about 350,000 people, the biggest protest in the capital Kiev since the "Orange Revolution" of nine years ago.

On a day which also marked the anniversary of Ukraine's 1991 referendum on independence from the Soviet Union, opposition leaders denounced Mr Yanukovich for walking away from a pact offered by the EU and swinging trade policy back towards Russia.

"They stole the dream," heavyweight boxer-turned-opposition politician Vitaly Klitschko told the crowds on Independence Square.

"If this government does not want to fulfil the will of the people, then there will be no such government, there will be no such president," declared Mr Klitschko - a contender for the next presidential election due in 2015.

After months of pressure from Russia, Mr Yanukovich backpedalled last week from signing the deal on closer relations with the EU in favour of renewed economic dialogue with Moscow.

Far-right leader Oleh Tyahniboh called for a national strike and members of his Svoboda (Freedom) party occupied Kiev's city hall along with followers of former economy minister Arseny Yatsenuk's Batkivshchyna (Fatherland) Party.

All three opposition leaders occupied a trade union building, turning it into a temporary headquarters.

The events, evoking memories of the 2004-5 Orange Revolution that overturned the established political order, took place against the background of an apparent attempt by a protesters to storm the main presidential office.

Interior Ministry forces and riot police fired tear gas and stun grenades to repel the protesters, who used an earth excavator in a bid to break through police lines.