The European Union has halted work on a trade agreement with Ukraine, an official said Sunday, after Kiev failed to show "clear commitment" to signing the deal.

Stefan Fule, European commissioner for enlargement and European neighborhood policy, said on Twitter that the words and deeds of Ukrainian President Viktor Yanukovych and his government on the proposed pact were "further & further apart. Their arguments have no grounds in reality."

Fule said he had told Ukrainian Deputy Prime Minister Serhiy Arbuzov in Brussels, Belgium, last week that further discussion on the agreement was conditional on a clear commitment by Kiev to sign the deal, but he had received no response.

"Work on hold, had no answer," he tweeted.

Last month, Kiev spurned the agreement in favor of closer economic ties with Moscow, sparking mass protests as thousands of people poured onto the streets of the capital, angered by the government's U-turn away from integration with Europe.

Setting up tents and barricades, they have stood their ground in Kiev's Independence Square, or Maidan, paralyzing the center of the capital.

On Sunday the protesters were addressed by U.S. Sen. John McCain, who has been critical of Ukrainian authorities' use of force against demonstrators.

"People of Ukraine, this is your moment. This is about you, no one else. This is about the future you want for your country. This is about the future you deserve," he said to loud cheers and chants of "Thank you."

"A future in Europe, a future of peace, with all of your neighbors. The free world is with you, America is with you, I am with you."

The senator visited Independence Square on Saturday, where he snapped pictures with his cell phone as he met with opposition leaders. He was accompanied on stage Sunday by Sen. Christopher Murphy, D-Connecticut.

"Ukraine will make Europe better and Europe will make Ukraine better," McCain said.

A pro-government rally was also being held Sunday.

The anti-government demonstrations are the biggest since the Orange Revolution overturned the results of the eastern European country's 2004 presidential election.

East vs. West

The EU had kept its offer on the table, and the bloc's top diplomat, Catherine Ashton, on Thursday said Yanukovych had assured her Kiev intended to sign the deal after she met with him.

A day earlier, Prime Minister Mykola Azarov told a government meeting Ukraine was still open to signing the European integration deal, if the European Union would agree to provide financial assistance to Ukraine of around 20 billion euros ($27.5 billion).

On Sunday however, an EU diplomat told CNN there was "lack of clear commitment and timetable".

"We have had no reply (on timetable) from the Ukrainian authorities and so there is no basis to continue work," the diplomat added.

Ukraine is split between pro-European regions in the west of the country and a more Russia-oriented east.

Protesters say an EU agreement would open borders to trade and set the stage for modernization and inclusion. They accuse Yanukovych of preparing to take the country into a Moscow-led customs union.

Moscow has leverage that may have affected Yanukovych's decision last month to backpedal on the EU talks because Russia supplies Ukraine with natural gas.

The EU is also pressuring Yanukovych to free his chief political opponent, Yulia Tymoshenko, who has languished in jail for two years after being convicted of abuse of power in 2011. The EU and other critics decried the verdict as a sham.

The Orange Revolution that swept Yanukovych from office in 2004 also brought the pro-Western Tymoshenko to power.

At the rallies in Independence Square, protesters have carried her picture.

Investigation

Kiev's handling of the protests has been met with stern responses from Western governments.

In an overnight crackdown last week, police tore down barricades the protesters had set up. Before that, violence had broken out at a previous demonstration.

Ukrainian prosecutors are investigating some top government officials over the beating of students at anti-government protests two weeks ago.

The subjects of the criminal investigation include Ukrainian Deputy Secretary for National Security Vladimir Sivkovich, Kiev Police Chief Valery Koryak and Kiev Mayor Oleksandr Popov. A fourth person also is under investigation.

The case will be put before a judge on Monday, who could order house arrest for those being investigated, said Valery Vilkova, spokeswoman for the general prosecutor.