The ongoing pro-European protests in Ukraine threatened to turn violent on Monday when police fired tear gas to disperse a crowd of protesters near a government building in the capital Kyiv.

The protesters have been active all night in the center of the capital, where they have built tents around European Square.

On Sunday, tens of thousands of Ukrainians took to the streets of the capital to protest the government's decision last week to scrap an EU trade treaty. 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.

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

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

Pressure from Moscow

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.

Protesters have been backed by the main opposition parties, the Ukrainian Democratic Alliance for Reform of boxer-turned-politician Vitaly Klitschko, and the party of jailed opposition leader Yulia Tymoshenko.

Along with the resignation of President Viktor Yanukovych, protesters have also called for the release of Tymoshenko, also one of the preconditions for the deal demanded by the EU.

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.

hc/tj (Reuters, AFP, AP, dpa)