In a televised announcement late on Friday, a member of Ukraine's SBU secret service, Maxim Lenko, said evidence gathered in a December raid on the offices of the opposition Fatherland party indicated that the opposition had instigated the protests, which led to the resignation of the prime minister and cabinet earlier in the week.
The news agendy Interfax quoted Lenko as claiming that the opposition had also provoked police violence against the demonstrators.
Four people were killed when the protests turned violent last weekend, three of which were victims of gunshot wounds.
The purported evidence apparently came from computers found in the raid on the Fatherland party. Ukraine's jailed former prime minister, Yulia Tymoshenko, is a member of that party.
According to unconfirmed reports, Tymoshenko's Fatherland party described the announcement as a provocation.
On television, Lenko said the anti-government protests had been "pre-planned," including "the use of force against protesters… to undermine the authority of the president," Viktor Yanukovych.
Ashton 'appalled' by apparent torture
The allegation came after opposition activist Dmytro Bulatov, who went missing more than a week ago, reappeared Thursday night, saying he was tortured by abductors who cut off his ear and drove nails through his hands before dumping him in a forest.
EU foreign affairs chief Catherine Ashton said she was "appalled" by the apparent torture inflicted on Bulatov while Amnesty International said the "barbaric" act should be immediately investigated.
Ukrainian protest movement leaders have claimed that abuse and beatings of activists have been widespread.
President Viktor Yanukovych, who has been on sick leave since Thursday, repealed draconian anti-protest laws passed in January on Friday.
Two months of anti-government protest erupted in November when the president backed out of a key pact with the European Union in favor of closer ties with Moscow.
On Friday, he also signed an amnesty bill for jailed opposition activists, but it will only take effect if protesters vacate the public buildings they have occupied within 15 days.
mz/ipj (AFP, dpa)