KIEV, Ukraine (CBS) -- About 200,000 anti-government protesters converged on the central square of Ukraine's capital Sunday, a dramatic demonstration that the opposition's morale remains strong after nearly four weeks of daily protests, but shadowed by suggestions that their goal of closer ties with Europe may be imperiled.
A much smaller rally of government supporters, about 15,000, was taking place about a kilometer away from Independence Square - familiarly called Maidan - where anti-government protesters have set up an extensive tent camp and erected barricades of snow hardened with freezing water and studded with scrap wood and other junk.
Protests began Nov. 21 after President Viktor Yanukovych announced he was backing away from signing a long-awaited agreement for Ukraine to deepen trade and political ties with the European Union and instead would focus on ties with Russia. The protests grew in size and intensity after two violent police dispersals of demonstrators.
In the face of the growing protests, which present a serious challenge to Yanukovych's leadership, Ukrainian officials this week renewed talks with the EU about signing the association agreement. Deputy Prime Minister Serhiy Arbuzov said Thursday that Ukraine would sign soon, once some issues were worked out.
However, the EU's top official on expansion issues, Stefan Fuele, cast doubt on the prospects on Sunday. Fuele said on his Twitter account that work on the agreement is "on hold" and that the words and actions of Yanukovych and his government regarding the agreement are "further and further apart."
Yanukovych backed off the association agreement on the grounds that the EU was not providing adequate compensation for the potential losses in trade with Russia that the economically struggling country would face under the pact. Russia, which for centuries controlled or exerted heavy influence on Ukraine, wants the country to join a customs union, analogous to the EU, which also includes Belarus and Kazakhstan.
The opposition says that union would effectively reconstitute the Soviet Union and remain suspicious that Yanukovych intends to agree to the customs union when he meets Russian President Vladimir Putin on Tuesday.
"What is happening on Maidan today? It is an anticolonial revolution. Above all, Ukrainians turned out to say to Moscow: 'we are no longer under your command, we are an independent country," Yuriy Lutsenko, a top opposition official and former Interior Minister, told the crowd.
U.S. Senators John McCain and Chris Murphy also addressed the crowd, expressing support for the protesters and their European ambitions.
"We are here because your peaceful process and peaceful protest is inspiring your country and inspiring the world," McCain said. "Ukraine will make Europe better and Europe will make Ukraine better."
That was a polar opposition to the views of many at the pro-government rally.
"We'll become the slaves of Europe if we go into it," said 43-year-old demonstrator Segei Antonovich. "Loook at history - only union with Russia can save Ukraine from catastrophe."
McCain also singled out the police, saying "we ask that you always be guided by your duty to protect your fellow citizens."
Over the past week, Ukrainian officials have made some steps toward the opposition, with Yanukovych proposing an amnesty for demonstrators arrested in the police break-ups of protests and suspending two senior officials under investigation for the violence.
The opposition, however, is holding to stronger demands, including the resignation of the government and early elections for both president and parliament.