Hundreds of people rallied to protest against what the Ukrainian opposition says was vote-rigging by President Viktor Yanukovich's ruling party in parliamentary elections.

Crowds gathered at the Central Electoral Commission in the Ukrainian capital in response to a call for protest by opposition parties, including that of jailed ex-prime minister Yulia Tymoshenko.

Police told the crowd the protest was illegal and might be broken up by force, but the threat was ignored by the demonstrators.

"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 heads the united opposition in the absence of Tymoshenko.

"We have gathered here to defend our choice, the choice of Ukraine and Ukrainians."

Tensions have focused on the outcome of a handful of constituencies where the vote-count for seats in the 450-seat parliament has not been completed.

Anger erupted at several disputed districts, with election officials conducting the vote-count besieged by opposition supporters and members of Yanukovich's Party of the Regions.