"What's happening today in Ukraine is the seizure by the political raiders of Putin's Russia of a sovereign state in the center of Europe," Saakashvili said, according to the Interfax news agency.
A vice president of the European People's Party, a continent-wide grouping of center-right parties, said in Kiev that Yanukovych "from the very beginning didn't want to sign it; he was thinking about Moscow."
Also Saturday, the Interior Ministry said police have placed the Kiev broadcasting center under heavy guard, saying the move was necessary after hearing protesters express intentions to march on the facility and block access to the building.
The center houses the studios of several TV channels, including the national First Channel, which on Saturday was hosting a show featuring an array of government ministers.
Snow and strong winds swept Kiev on Saturday and the crowd at Independence Square, the main protest site and home to a round-the clock tent camp, numbered only several thousand. But organizers have called for a massive rally on Sunday. A similar call a week ago brought out a throng estimated at more than 300,000.