Nearly 300,000 outraged Ukrainians braved freezing temperatures Sunday to demand closer Western integration after the European Union abruptly suspended historic partnership talks because of the government's continued courtship of Russia.

The ex-Soviet nation of 46 million has been at the heart of a furious diplomatic tug of war since President Viktor Yanukovych's shock decision last month to ditch a landmark EU association agreement and seek closer ties with its traditional masters at the Kremlin.

EU Enlargement Commissioner Stefan Fuele announced in a surprise tweet at the start of Sunday's rally that the bloc was halting all negotiations until it received "a clear commitment" from Yanukovych that Ukraine was serious about the deal.

"Ukraine: Words and deeds of President and government regarding #AssocAgreement further and further apart," Fuele said.

Yanukovych is due in Moscow on Tuesday for talks with Russian President Vladimir Putin that protesters occupying central Kiev's iconic Independence Square fear could result in an even firmer alliance between the two neighbours.

Demonstrators have planned another huge rally to coincide with Yanukovych's meeting with Putin on Tuesday evening. They were warmly reassured of continued US backing on Sunday by Republican Senator John McCain -- one of Washington's staunchest critics of Kremlin rule.

"To all Ukraine, America stands with you," McCain called out to a cheering sea of people who chanted "Thank you!" in English in return.

McCain's travelling companion, Democratic Senator Chris Murphy, wrote on Twitter that Yanukovych had requested a meeting with him and McCain later that evening.

On Sunday evening, around 5,000 people stayed on the square, huddled around braziers or in canvas tents as temperatures fell to zero degrees celsius (32 degrees Fahrenheit).

Protesters were eagerly awaiting McCain's appearance onstage on Independence Square when news spread that Fuele had said Brussels was halting talks with Kiev after an inconclusive Friday meeting.
'Work on hold'

EU officials told Ukraine that further discussions required a "clear commitment (to) sign (but) Work on hold, had no answer," Fuele said.

Yanukovych upset Brussels on Friday by threatening to prosecute Ukrainian government officials who had worked out the current terms of the EU partnership deal.

The president then accused his negotiators of "violating the national interests" of Ukraine by putting the country's wobbling economy under further threat.

"Need clarity from #Ukraine whose President said it hurts national interests," Foreign Minister Linas Linkevicius of EU chair Lithuania tweeted on Sunday.

Prime Minister Mykola Azarov last week requested a 20 billion euro ($27.5 billion) loan from the European Union before it signs the closer trade and political association deal.

Ukraine says the money would compensate for the losses it would suffer from the trade sanctions threatened by Russia -- an energy power that has promised cheaper gas shipments should Kiev join a customs union championed by Putin instead.

Brussels has rejected the loan request and argued that Ukraine stood to benefit over the long term from the removal of EU trade barriers.

Swedish Foreign Minister Carl Bildt -- a strong proponent of Ukraine's integration who has paid repeated visits to Kiev -- said Sunday that the original terms of the EU deal stood.

"The door is wide open for Ukraine to sign association and free trade agreement with EU," Bildt tweeted. "It's ready. Any time."

Rival rallies

Ukraine's security services were on high alert on Sunday as around 5,000 Yanukovych supporters bused in from the provinces began what they said would be "nonstop protests" in a park near Independence Square.

"If the president made a mistake, that doesn't mean you need to gather in the Maidan (Independence Square)," said pensioner Galina Beresneva as she stood amid dozens of large army tents and a field kitchen set up by pro-government organisers.

Yanukovych moved to appease the protest movement on Saturday by suspending Kiev's mayor and the deputy head of his security council over a violent November 30 crackdown on protesters.

But opposition leaders said they were also seeking the dismissal of the interior minister and the prime minister.

McCain began his visit to Kiev on Saturday by holding meetings with the troika of opposition leaders who most prominently include boxing champ turned UDAR (Punch) party leader Vitaly Klitschko.

The powerful US senator declared Sunday that Ukraine's protests -- the largest since the 2004 pro-democracy Orange Revolution -- were "inspiring" the entire world.

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

A 56-year-old electrician named Sergei said he and others around him on Independence Square felt encouraged by McCain's talk.

"Of course it's important to have the support of the American parliament and president," Sergei said. "In Ukraine we don't think the US wishes us harm."