An estimated 70,000 pro-Western Ukrainians have thronged the heart of Kiev vowing never to give up their drive to oust President Viktor Yanukovych over his alliance with old master Russia.
Opposition leaders on Sunday addressed a crowd of supporters wearing blue and yellow ribbons - the colours of both Ukraine and the European Union - on the central Independence Square in a bid to ratchet up pressure on Yanukovych to appoint a new pro-Western government.
READ MORE: Timeline of the Ukrainian political crisis
"None of the kidnappings and tortures have yielded any results," said Igor Lutsenko, an activist who survived a severe beating after reportedly being abducted from hospital during deadly unrest in January.
The ex-Soviet nation of 46 million people has been in chaos since November when Yanukovych ditched an historic EU trade and political pact in favour of closer ties with Moscow, stunning pro-EU parts of the population and sparking violent protests.
Since then, what started out as a localised, domestic bout of unrest has snowballed into a titanic tussle for Ukraine's future between Russia and the West, as demonstrations continued and spread to other parts of the country.
Ukraine's state security service announced Sunday that anti-terrorist units had been placed on high alert due to increased threats against key sites such as airports, stations, pipelines and nuclear plants.
The SBU counterintelligence agency said the measures were "primarily preventative" and made no explicit reference to the mass protests.
But it mentioned "threats of explosions" at strategic transport hubs and energy installations as well as "calls to occupy sites sheltering large stocks of weapons" and the "blockading of government buildings".
The protesters who have been occupying central Kiev for more than two months have seized several state buildings and repeatedly clashed with police.
After initially ignoring protesters' demands, Yanukovych has recently yielded ground by dismissing the government.
But he also has to appease Russia, which has effectively frozen a sorely-needed $US15 billion ($A16.80 billion) bailout until the situation clears up.
READ MORE: An insider's look at the protests in Kiev
Moscow has so far issued only one $US3 billion instalment of the loan, which it promised to Yanukovych after he rejected the EU pact.
The protest - which ended without violence - is the 10th major demonstration since November, and the size of the crowds Sunday roughly equalled the turnout last weekend, although it was markedly lower than at the end of January, when violence left several people dead and hundreds injured.
