Ukraine crisis: Opposition MPs seek to curb president's powers
Ukraine's MPs are continuing crisis talks to try to change the constitution - a move aimed at curtailing the powers of President Viktor Yanukovych.
This is a key demand by the opposition, who has warned that parliament's failure to act now will further inflame mass anti-government protests.
Pro-presidential MPs oppose the move, and the speaker has given until Wednesday morning to find a compromise.
Kiev's decision to reject an EU deal in November triggered the protests.
The battlefield in Ukraine's political stand-off has shifted once again this week from the country's streets, squares and government buildings to parliament - the Verkhovna Rada.
Opposition leaders seem to believe that, this time, they can convince enough pro-government deputies, or the communist party faction as a whole, to break ranks - thereby giving the anti-government forces the votes they need - and vote for a return to the 2004 constitution.
If they were to succeed, it would be a major victory: President Viktor Yanukovych's powers would be restricted considerably and presidential elections would take place sometime this year.
But up to now, the opposition has been unable every time to assemble a majority.
And judging from the impassioned and uncompromising speeches coming from deputies of Mr Yanukovych's Regions Party during Tuesday's opening session, it would appear that so far, the anti-government forces have failed again.
At least six people have died in violence since then, and a number of Ukrainian politicians have warned that the country might plunge into civil war.'Stop dictatorship'
The opposition is pushing for a return to the 2004 constitution, which would mean President Yanukovych losing some of the powers he has gained since his election in 2010.
The changes envisage that parliament - not the president - will be appointing the prime minister and cabinet members as well as regional governors.
There were emotional scenes earlier on Tuesday and MPs began debating the issue.
"I call on everyone to take the constitutional route and stop dictatorship," the leader of the opposition Udar (Punch) Party and former world heavyweight boxing champion, Vitaliy Klitschko, told parliament.
"Let us reinstate the constitution that allows MPs to take decisions instead of just pushing buttons."
Mr Klitschko also stressed that snap presidential elections were crucial to regain the trust of the people.
But the leader of President Yanukovych's Regions Party in parliament, Oleksandr Yefremov, accused the opposition of being irresponsible.
"They (opposition leaders) are fighting not for what people want, but for power," he said in a speech delivered amid shouting.
"Ukraine is going through perhaps the most dramatic period in its recent history. Any further escalation of the conflict may lead to civil confrontation and result in catastrophic consequences," he added.
At one point during the proceedings, some opposition MPs shouted "murderers!".
They were referring to the death of protesters over recent weeks as anti-government activists clashed with riot police.
Protesters blame the government for the deaths, but officials reject these accusations.
Later on Tuesday, the speaker of parliament, Volodymyr Rybak, gave lawmakers until 10:00 local time on Wednesday (08:00 GMT) to try to find a compromise on the constitutional changes.Marshall plan plea
However, correspondents say party allegiances have been fluid and it is unclear if the opposition can rally a majority in parliament over the issue.
Ukraine unrest: Timeline
21 November 2013: Ukraine announces it will not sign a deal aimed at strengthening ties with the EU, sparking protests
17 December: Russia agrees to buy $15bn of Ukrainian government bonds and slash the price of gas it sells to the country
16 January 2014: Parliament passes law restricting the right to protest
22 January: Two protesters die from bullet wounds during clashes with police in Kiev; protests spread across many cities
25 January: President Yanukovych offers senior jobs to the opposition, including that of prime minister, but these are rejected
28 January: Parliament votes to annul protest law and President Yanukovych accepts resignation of PM and cabinet
29 January: Parliament passes amnesty law for detained protesters, under the condition occupied buildings are vacated
Mass unrest began when President Yanukovych abandoned an association and free trade deal with the EU in favour of closer ties with Russia.
Thousands of people remain encamped in Kiev's heavily fortified Independence Square - widely known as the Euromaidan. Protesters in the capital and in a number of Ukraine's regions have also occupied some government buildings.
Under pressure from the opposition, Mr Yanukovych last week scrapped anti-protest laws and accepted the resignation of Prime Minister Mykola Azarov and the cabinet.
But his opponents want him to resign before the end of his mandate in 2015 and to call early elections.
EU foreign policy chief Catherine Ashton will return to Kiev on Tuesday and US Assistant Secretary of State Victoria Nuland is due to visit later this week.
Their visits come after Arseniy Yatsenyuk, one of the leaders of the Fatherland opposition party, asked for a "Marshall Plan" for Ukraine - a reference to the US aid package for Europe after World War Two.
The US state department said Washington and Brussels were in preliminary discussions on financial help for Ukraine if a new, technocrat government was formed.
Moscow, which has conditionally offered a $15bn (£9bn) aid package to Ukraine, has criticised the EU and other Western countries for intervening in the dispute.