KIEV, Ukraine — About 200,000 anti-government protesters converged on the central square of Ukraine’s capital Sunday in a dramatic show of morale after nearly four weeks of daily protests, but the rally was shadowed by suggestions that their goal of closer ties with Europe may be imperiled.

A much smaller demonstration of government supporters, about 15,000, was taking place about less than a mile away from Kiev’s Independence Square. Anti-government protesters have set up an extensive tent camp there and erected barricades of snow hardened with freezing water and studded with scrap wood and other junk.

U.S. Sens. John McCain and Chris Murphy joined the anti-government demonstration to express support for the protesters and their European ambitions, threatening sanctions against the government of President Viktor Yanukovych if authorities use more violence to disperse the protests.

The protests began Nov. 21 after Yanukovych announced he was backing away from signing a long-awaited agreement to deepen trade and political ties with the EU and instead focus on Russia. They have grown in size and intensity after two violent police dispersals.

In the face of the protests, which present a serious challenge to Yanukovych’s leadership, Ukrainian officials this week renewed talks with the EU agreement and promised that they would sign the deal once some issues are worked out.

However, the EU’s top official on expansion issues, Stefan Fuele, said that work is “on hold” and that the words and actions of Yanukovych and his government are “further and further apart.”

Yanukovych says the EU would not provide his nation adequate compensation for potential trades losses with Russia.