The rally, the biggest this year in a cycle of pro-Europe protests convulsing the former Soviet republic for the past two months, was spurred by the legislation rushed through parliament last week and which the opposition says will lead to a police state.

Significantly raising the stakes in the confrontation with President Viktor Yanukovich, opposition leaders announced a plan to gather people's signatures expressing no confidence in his leadership and that of parliament.

Denouncing as unconstitutional last Thursday's hurried vote in parliament by Yanukovich's supporters, they called for moves to set up a parallel structure of power - including a people's assembly and a new constitution.

"Yanukovich and his henchmen want to steal our country. Ukraine is united as never before in its struggle against those in power today, in its determination not to allow a dictatorship," declared boxer-turned politician Vitaly Klitschko, the strongest potential challenger for the presidency.

Though setting up an alternative power structure may not be realistic, Sunday's turn-out suggested it could also be difficult for the authorities to try to solve the crisis by use of force despite the court ban and the new laws.

Another opposition leader, far-right-nationalist Oleh Tyahnibok, dismissed the laws as unconstitutional as he spoke from the tribune on Kiev's main Independence Square.

"So we have a right not to carry them out and we will sabotage them," he said.

Yanukovich triggered the pro-Europe rallies when he did an about-turn last November and ditched a free trade deal with the European Union in favor of closer economic ties with Ukraine's former Soviet overlord, Russia.

This brought tens of thousands of people on to the streets and protesters set up a permanent encampment on Independence Square. Though numbers have dwindled since, several hundred people remain camped out there or are occupying buildings such as City Hall.

The court ban on protests published on Jan. 15 and last Thursday's legislation aimed at prohibiting all form of public protests inflamed tensions again.

The laws - denounced by the United States and other Western governments as anti-democratic - would ban any unauthorized installation of tents, stages or use of loud-speakers in public places.

They banned, under pain of heavy jail sentences, participation in "mass disorder", banned the wearing of face-masks or protective helmets and outlawed dissemination of "extremist" or libelous information about the country's leaders.

As well as showing the opposition's enduring support, Sunday's protests further enshrined Independence Square as the platform from which Yanukovich's foes will campaign against him ahead of a February 2015 election.