KIEV: Ukrainian President Viktor Yanukovych was set to return to work on Monday from four days of sick leave after opposition leaders demanded he accept curbs on his power and appealed for Western aid.

As he recovers from an “acute respiratory infection” which critics dismissed as a ploy to win time, the president has to choose between making further concessions to the pro-EU protest movement or clamp down after two months of protests.

Following talks with top Western officials including US Secretary of State John Kerry and EU foreign affairs head Catherine Ashton in Munich over the weekend, opposition leaders including boxer-turned-politician Vitali Klitschko have urged the West to mediate in talks with Yanukovych.

Convening tens of thousands for a new rally at Kiev's barricaded tent city on Independence Square amid freezing temperatures on Sunday, the protest leaders also requested “real financial aid.”

Former economy minister Arseniy Yatsenyuk, who turned down Yanukovych's proposal to serve as prime minister, said Western officials had assured him that funding was on its way.

“They are ready to do it,” he told the crowd.

EU's Ashton told The Wall Street Journal in an interview published Sunday that Western countries were considering a financial package for Ukraine that “won't be small”.

She said the plan would depend on the Ukrainian government's willingness to pursue economic and political reforms.

Yatsenyuk has said Ukraine, which is mired in deep economic trouble, needs a 'Marshall Plan' from the West, referring to the Cold-War initiative which saw the United States help rebuild Europe after World War II to prevent the spread of Communism.

Russia has expressed fury over what it calls foreign interference in its Soviet-era satellite's domestic affairs.

Russia in December pledged a $15 billion bailout package and gas supplies discounts for Kiev.

President Vladimir Putin said last week however the financing was on hold pending the formation of a new government in Ukraine following the resignation of Kremlin-friendly Prime Minister Mykola Azarov.

The Kremlin has publicly supported Yanukovych, dismissing the protesters as far-right extremists, antagonising protesters further.

“Moscow is waiting for the right moment to organise a Ukraine split and destroy the country's territorial integrity,” leader of nationalist Svoboda (Freedom) party, Oleg Tyagnybok, told the rally on Sunday.

Over the past few weeks, the protests have expanded beyond the capital and the traditionally pro-opposition western Ukraine into pro-Yanukovych, Russian-speaking central and eastern parts.

The opposition plans a new series of pickets across the country from Monday.

Ukraine's worst political crisis since its 1991 independence, which has pitted Russia against the West, broke out after Yanukovych ditched a key pact with the European Union in November.

The protest movement has recently radicalised and turned into a drive to oust the 63-year-old leader.

The opposition leaders fear Yanukovych may introduce a state of emergency and move the army against demonstrators.

Tortured militant leaves Ukraine

The opposition claims beatings and abuse of protesters are widespread.

A prominent Ukrainian protester, whose account of torture has shocked Europe, left Ukraine for treatment in Lithuania on Sunday.

Dmytro Bulatov, 35, said he was “crucified” by his unidentified captors before being released in a forest last week.

Ukrainian authorities have cast doubt on the veracity of his story and Foreign Minister Leonid Kozhara dismissed his injuries as “a scratch” before retracting the comment.

The case has been highlighted by the opposition as an example of what it says is a “secret repression” against protesters in which pro-government vigilantes have been employed.

Yanukovych has offered the opposition a series of concessions including the scrapping of hugely controversial anti-protest laws.

But the protest leaders are calling for a constitutional overhaul to take away the sweeping powers that Yanukovych has accumulated during his rule and give more weight to the government and parliament.

They also want the immediate and unconditional release of activists detained during the demonstrations and for Yanukovych to announce early elections.

According to official figures, four people — two protesters and two policemen — were killed at the height of the clashes last month that turned parts of central Kiev into a veritable war zone.