KIEV, Ukraine -- A showdown between Russia on one side and the United States and the European Union on the other drew closer here Sunday, as two American senators told a crowd of hundreds of thousands of protesters that Ukraine's future lies to the west, not the east.
"We are here," said Sen. John McCain, R-Ariz., "to support your just cause: the sovereign right to determine Ukraine's own destiny freely and independently. And the destiny you seek lies in Europe."
Added Sen. Chris Murphy, D-Conn.: "Ukraine's future stands with Europe, and the U.S. stands with Ukraine."
"Molodtsi," the crowd chanted in Ukrainian, indicating its approval. But the president whom the opposition so despises, Viktor Yanukovych, is heading Tuesday for Russia to cement deals involving natural gas purchases and financial credits to prop up his country's ailing economy.
Mr. Yanukovych has vowed that he will not commit Ukraine to Russian President Vladimir Putin's new Eurasian Customs Union, but the Ukrainian opposition doesn't believe him.
Mr. Murphy, Mr. McCain and European politicians who addressed the crowd in Kiev on Sunday turned up the pressure on Mr. Yanukovych, promising that their governments will consider individual financial sanctions against responsible Ukrainian officials if there is any further outbreak of police violence against the protesters who come and go at the semi-permanent encampment on Kiev's Independence Square.
Mr. Yanukovych has tried to mollify the opposition by resuming talks with the EU on a trade agreement. His Nov. 21 decision to back away from the deal triggered the protest movement.
But in Brussels on Sunday, the EU commissioner for expansion, Stefan Fule, announced on Twitter that he was suspending negotiations with Ukraine on a revised trade agreement because Mr. Yanukovych's words and actions on the issue were "moving further and further apart."
Ukraine's arguments in favor of better terms than those agreed to earlier this year have "no grounds in reality," Mr. Fule wrote.
Still, Elmar Brok, a member of the European Parliament, told the crowd in Kiev, "The door for Ukraine to Europe is open."
Opposition leaders are concerned that if Mr. Yanukovych signs an agreement on Ukraine's eventual membership in Russia's Eurasian Customs Union, that would remove the possibility of a pact with the EU.
"If the agreement is signed, he can remain in Moscow and not return to Kiev," Arseniy Yatsenyuk, head of the Fatherland party, said from the stage here Sunday.
Demonstrators have turned out for three weeks in the encampment on Independence Square, expanding the scope of their protest to denounce police violence and political corruption. The protesters insist that they will not leave until Mr. Yanukovych is booted out of office. But it is unclear which side in the fight for Ukraine's future has more stamina and resolve.
The government is "expecting cold weather to break people's spirits," said Yakov Hutsul, 29, who runs an air-conditioning business in Ternopil, in western Ukraine. "But we'll be here. Cold weather is not the main evil we're contending with. There is no way back."
With the temperature hovering around freezing, Sunday's turnout appeared to be somewhat smaller than a huge rally a week earlier, but news agencies estimated that it still drew about 200,000 people, bedecked in hats, scarves and Ukrainian flags.
A smaller rally of about 15,000 people, also arrayed in Ukrainian flag paraphernalia, showed its support for Mr. Yanukovych in a hilltop park near the parliament building. "We're here so this can all end peacefully," said Lyudmila Akhmedzhanova, 50, a teacher who, unusually for a Yanukovych supporter, comes from western Ukraine. "And we're here for the European Union."
She said that she was not opposed to an eventual alliance with the European Union but that now was not the time. "We're supporting Yanukovych because we need to wait a little," Ms. Akhmedzhanova said. "With time, we can come to a European level."
Solid lines of police vehicles and heavily armored officers separated the two rallies Sunday. No serious incidents were reported.
Mr. McCain commended veterans of the Soviet war in Afghanistan who have been helping to defend the protest site. "Ukraine will make Europe better," he said, "and Europe will make Ukraine better."