Demonstrators waving European Union and opposition party flags marched through central Kyiv on Sunday in protest at last week's decision by the government not to sign an Association Agreement with the EU.

An estimated 50,000 people took part in the protest, making it the largest Ukraine has seen since the peaceful 2004 Orange Revolution.

Some held posters saying "We are not the Soviet Union, we are the European Union." Protesters also called for President Viktor Yanukovych to step down and for the release of jailed opposition leader Yulia Tymoshenko

Tymoshenko, whose release is also one of the preconditions for the deal demanded by the EU, called for the street protests after the government scrapped plans to sign the agreement.

Yanukovych only narrowly defeated Tymoshenko in the 2010 presidential election and sees her as a political threat. There are western concerns her prisonment is politically motivated.

Pressure from Russia

Ukraine's leaders announced suddenly on Thursday that they were pulling out of the deal on free trade and political association with the EU, saying the country could not afford to break trade ties with Russia.

The deal was due to be signed at a key summit in the Lithuanian capital Vilnius this week.

Ukraine's economy has shrunk for five successive quarters. The country's immediate economic plight is seen by analysts to have been one of the factors in the government's decision to shun the EU deal, whose benefits would be obvious only in the long term.

Moscow, which envisages Ukraine as part of a Russian-led Customs Union and is a major trading partner, had threatened trade retaliation if Kyiv signed the deal.

Signing the accord would have put Ukraine on the path to eventual EU membership and drawn the former Soviet state out of Russia's orbit.

tj/ccp (AFP, AP)