The demonstrators gathered outside of the Central Electoral Commission in the capital, Kyiv, after opposition parties called on their supporters to protest against the October 28 election, which they say was rigged.
Although final results have not yet been published, with more than 99 percent of the votes counted, President Victor Yanukovich's Party of Regions appeared set to scrape through with a reduced majority. The voting still has not been completed in a number of electoral districts, some of which are at the heart of the opposition's accusations.
"The Party of the Regions is simply stealing the votes of Ukrainians and registering them as the votes of the candidates of the party in power," said Arseny Yatsenyuk, who currently leads united opposition movement in the absence of jailed former Prime Minister Yulia Tymoshenko.
"We have gathered here to defend our choice, the choice of Ukraine and Ukrainians. Ukraine has shown that it is capable of beating the Party of the Regions," he told the crowd.
The crowd was met by police in riot gear who threatened to break up the rally by force if the demonstrators failed to disperse. The protesters though, stood their ground.
The opposition is calling for a recount in the electoral districts where the results are disputed and has threatened to boycott the new parliament if it doesn't get its way. The election commission gave into recount demands in five districts, buts said parliamentary approval was required.
The fact that the results still haven't been published several days after the election has also raised eyebrows in Brussels.
On Saturday, the European Union's (EU) foreign policy coordinator, Catherine Ashton, and its enlargement commissioner, Stefan Fule, issued a joint statement calling on "authorities and all parties involved to take the necessary steps to finalise the tabulation allowing for the rapid announcement of the final results, which should reflect the genuine will of the Ukrainian voters."
Relations between the EU and Ukraine have been strained since last year, when Tymoshenko was convicted and sentenced to seven years in jail for abuse of office. The EU responded by putting an association agreement with Kyiv on ice.
pfd/msh (AFP, Reuters, AP)