Ms. Zorina said that President Viktor F. Yanukovich was acting out of selfishness and self-interest in deciding not to sign the agreements with the European Union. “He’s more interested in his own business dealings with Russia,” she said.

The political and trade accords, which had been in development for more than four years, had been scheduled to be signed later this week at a major conference in Vilnius, Lithuania. But, on Wednesday, the Ukrainian government announced that it had suspended its plans to complete the agreements.

On Sunday evening, several thousand protesters were engaged in a standoff with a phalanx of police outside the Cabinet of Ministers building. Some tussled with the officers, who were wearing gas masks, and tear gas was sprayed, but it was unclear whether the police or protesters had used it. At one point, a lit flare was thrown at the police in gas masks who were blocking access to the building, and a flagpole was knocked down.

The police reacted with restraint and there were no immediate reports of arrests. Some demonstrators, however, said that tension was building.

“The situation in society is boiling,” said Svyatoslav Tseholko, a television host and chief projects editor of Ukraine’s Channel 5, who attended the demonstration wearing a blue-and-yellow ribbon. “And we don’t know when is the time the top will pop off.”