Addressing a rally of some 10,000 supporters in central Kiev, Klitschko renewed calls for the European Union to impose sanctions on the country's leadership.
"Moral support for opponents of the government is not enough," he said.
The former champion boxer - who heads the Udar (Punch) party - said he hoped that, after the forthcoming Orthodox Christmas, there would be a new wave of protests leading to a general strike against the government of President Viktor Yanukovych.
Sunday's rally, in Kiev's Independence Square, was the latest in a series of similar demonstrations that have been taking place since November.
Opponents of the government have been angered by its decision to freeze a wide-ranging trade agreement with the EU and to seek closer ties with Russia instead.
The government says it still wants to sign an agreement with the EU.
Klitschko's party is the second-biggest opposition force in Ukraine, after the Fatherland party of jailed former premier Yulia Tymoshenko.
Source: Sydney 7 News