Russia warns Ukraine opposition as protests continue
Russia has urged Ukrainian opposition leaders to end their campaign of "ultimatums and threats" and to step up negotiations with the government.
Russia's foreign ministry said Moscow was concerned by activists' attempts to "inflame" the situation.
Protesters in Kiev have repeated their calls for the resignation of President Viktor Yanukovych, who is now back at work after four days of illness.
The EU and US are considering a big loan to help debt-laden Ukraine.
Western officials for the most part have followed a policy of reaction in dealing with events in Ukraine, ever since President Viktor Yanukovych's surprise cancellation of landmark agreement with the EU unleashed the anti-government Euromaidan movement.
Now, however, Washington and Brussels seem to have taken the initiative. A prospective joint EU-US financial aid package, announced in the Wall Street Journal, is intended to encourage reforms and a peaceful resolution in the country's protracted political standoff.
It's an understatement to say that the plan depends on a number of variables. President Yanukovych's acceptance of the plan - if it is offered - is one of the main ones. Another is the reaction to the protesters on Kiev's streets, who might not welcome the possibility of a "national unity" government, which leaves Mr Yanukovych in power.
It's a "big carrot," one senior US official was quoted as saying. The next weeks will show if it is indeed what is needed.
"We are looking at how we could support the Ukraine in the times of the crisis when it comes to the economic and political situation," a spokeswoman for EU foreign policy chief Catherine Ashton said on Monday.
No further details of the plan have been revealed, but both EU and US officials said it would be conditional on Kiev embracing "real reform".
European Commission President Jose Manuel Barroso insisted that the EU was not going to enter into a "bidding competition" with Russia to win Ukraine's loyalty.
Russia promised a $15bn (£9bn) aid package to Ukraine last year, but has indicated the next tranche will not be given until a new government is formed, following the resignation of the prime minister and cabinet last week.'Deep crisis'
Ukraine's unrest began in November, when President Yanukovych backed away from a planned trade deal with the EU, and instead agreed a loan with Russia.
The move sparked large scale protests in Kiev, which worsened and became deadly after new anti-protest laws were briefly put in place in January.
On Sunday, thousands of people joined a new rally in the centre of the capital, Kiev, with opposition leaders calling for international help.
The Russian foreign ministry denounced their actions in a statement on Monday, saying they were particularly "puzzling" in the wake of a summit held in Munich last week on Ukraine's future.
"We expect the opposition in Ukraine to avoid threats and ultimatums and step up dialogue with the authorities in order to finding a constitutional way out of the country's deep crisis," the foreign ministry said.'No to extremism'
Mr Yanukovych had been on sick leave since last Wednesday. His office said he had been suffering from a fever and breathing problems.
Opposition leaders had previously expressed scepticism about his illness, accusing him of trying to play for time.
In a statement on Monday on his return to work, he said Ukraine had to "say no to the extremism, radicalism and incitement to hatred in society, behind which lies a struggle for power".
He criticised the "vandalism" and occupation of government buildings by protesters in recent weeks, saying "the calls that we are hearing, they remind us of course of old history lessons. We do not want them to be repeated."
The president's first task on returning to work is to name a new prime minister to replace Mykola Azarov who resigned last week, along with his cabinet.
The government has offered a number of concessions, including repealing the controversial anti-protest laws and passing an amnesty for detained protesters.
But the demonstrators, who want to see closer ties with the EU rather than Russia, have not been placated and are demanding the resignation of the president, followed by elections.
On Tuesday, parliament will debate calls for a broader amnesty, and for a return to a previous constitution, which will restrict the powers of the presidency.
Meanwhile, the severely injured Ukrainian opposition leader Dmytro Bulatov has arrived in Lithuania for medical treatment.
Mr Bulatov appeared on TV last week saying he had been abducted and tortured.