By Li Hongmei

The European Union said on Sunday it was halting work on a landmark trade and political pact with Ukraine, hardening their rift even as tens of thousands took to the streets of Kiev urging President Viktor Yanukovich to mend ties with Brussels.

EU enlargement chief Stefan Fuele said on Twitter the words and deeds of Yanukovich and his government on the deal were "further and further apart".

His announcement came as 200,000 people braved sub-zero temperatures in Kiev to rally for the fourth weekend in a row against Yanukovich's decision not to sign the EU pact at a summit last month and concentrate instead on closer ties with Russia.

The EU had kept its offer on the table but Fuele said on Sunday the Ukrainian government's subsequent arguments on the terms of the deal had "no grounds in reality". "Work on hold," he added.

Fuele's words suggested the EU has lost patience with Kiev's demands for financial aid and was irritated at the way the bloc was being forced to take part in a 'bidding war' with Russia over Ukraine.

The focus was now on a visit Yanukovich is due to make to Moscow next Tuesday to tie up trade agreements with the Kremlin to help the distressed Ukrainian economy.

The opposition fears he may take the first steps towards joining a Moscow-led customs union, together with Belarus and Kazakhstan, which they see as an attempt by President Vladimir Putin to re-create the Soviet Union.

Protesters called for another mass rally on Tuesday to monitor Yanukovich's trip to Moscow. Prime Minister Mykola Azarov said late on Sunday he expected a deal on lower prices for Russian gas deliveries to Ukraine.

Yanukovich may be attempting to keep the attention of both Moscow and Brussels to strike as good a deal as possible to handle its huge debt and outstanding gas payments to Moscow. But it is a hazardous manoeuvre running the risk of alienating both parties.

The anti-government protesters received powerful encouragement on Sunday as U.S. Senator John McCain addressed the crowd on Kiev's Independence Square, telling them their destiny lay in Europe.

Street protests erupted after Yanukovich's decision on Nov. 21 to walk away from the agreement with the EU, after years of careful preparation, and turn to Moscow, Kiev's Soviet-era overlord, for aid to save Ukraine's economy.

Yanukovich's policy swerve, while backed by many in Russian-speaking east Ukraine which is his powerbase, disappointed and angered many in western and central areas where people feel close ties to Europe.

The presence of McCain at the anti-government rally after a weeks-long stand-off between demonstrators and the authorities further highlighted the geo-political East-West tug-of-war with Ukraine at its centre.

The Republican senator is the latest of a string of European and American dignitaries to tour the sprawling protest camp set up behind barricades of benches, metal barriers, supermarket trollies and wire netting on the square - known locally as the 'maidan'.

Russian Prime Minister Dmitry Medvedev has accused Western politicians of "crude" meddling in Ukraine.