Ukraine's president and parliament have agreed to implement a series of opposition demands in a bid to end the country's deadly political crisis.
Parliament voted on February 21 to amend the criminal code in a way that could allow for the release of jailed opposition leader Yulia Tymoshenko; to restore Ukraine's 2004 constitution; to implement an amnesty for opposition protesters facing possible prosecution; and to dismiss the interior minister.
Separately, President Viktor Yanukovych and opposition leaders have signed an agreement that is expected to lead to an early presidential election and talks on the formation of a unity government.
The European Union and the United States, which have backed the opposition throughout the crisis, have welcomed the moves and called for their swift implementation.
Russia, which backs the government, warned against further foreign interference in Ukraine and urged a national referendum on any constitutional changes. The Foreign Ministry said Moscow was ready to provide continued assistance to Ukraine.
Reverting to the 2004 constitution had been a key demand of the antigovernment movement. It was overturned by the Constitutional Court in 2010, after Yanukovych had taken office.
The 2004 constitution removes some powers from the presidential office, and enhances the powers of parliament.
EXPLAINER: Can Deal Reached End The Crisis?
The deal was signed by Yanukovych and opposition leaders Oleh Tyahnybok, Vitali Klitschko, and Arseniy Yatsenyuk at the presidential headquarters in Kyiv, with envoys from Germany, France, and Poland alsoin attendance.
A Russian presidential envoy who had flown to Kyiv to help mediation efforts was not present for the signing. The reason for Vladimir Lukin's absence was not immediately clear.
WATCH: Antigovernment protesters in Kyiv honor those who died in the violence on February 19-20 (natural sound).
The rapid-fire series of developments came after days of fighting between security forces and government opponents on the streets of Kyiv. Officials said around 80 people had been killed, mostly demonstrators but also security forces, and hundreds injured.
Yanukovych on February 21 announced two days of national mourning for the victims of the clashes.
After signing the agreement with Yanukovych, Klitschko said: "The priority today is to stop the bloodshed. This is the first aim. Our second aim is to do everything possible to punish those guilty of these events. Third, to do everything possible to prevent the country from splitting up."
The agreement calls for the formation of a national-unity government within the next two weeks. According to the pact, constitutional reforms are to be completed in September, with an early presidential election held no later than December.
In the case of Tymoshenko, parliament voted to decriminalize the statute under which she was imprisoned, meaning, according to reports, that she is no longer guilty of a criminal offense, thus enabling her release.
Tymoshenko's lawyer, Serhiy Vlasenko, said the entire procedure might take up to two weeks. Once free, Tymoshenko will be able to run for political office again because she will have no criminal record, he added.
Former Prime Minister Tymoshenko narrowly lost to Yanukovych in the 2010 presidential election. In 2011, she was sentenced to seven years in prison for abuse of office, in a case Western governments have condemned as a politically motivated attack by her opponents.
The opposition had also sought the restoration of the 2004 constitution. Under that charter, the presidential office has less powers than currently, while parliament has enhanced authority. The power to nominate a prime minister, for example, is in the hands of parliament.
Polish Foreign Minister Radoslaw Sikorski, who flew to Kyiv with the German and French foreign ministers to mediate, said the agreement will renew opportunities for Ukraine to strengthen ties to the West.
"Let us not forget what this crisis started with: it started with the disappointed hopes of millions of Ukrainians who wanted for their country a closer relationship with the European Union," Sikorski said.
"This agreement is not the end of the process, it is the beginning of the process but it makes it possible, imaginable again and that's why I am satisfied that after the horrible days in which so many people died, perhaps, there is a chance that they didn't die in vain."
LIVE BLOG -- Crisis In Ukraine
The reaction of opposition supporters to the deal wasn't immediately clear. These latest developments come after several days of deadly street violence in Kyiv, which included gunbattles between security forces and opponents of the government.
On February 21, Ukraine’s Health Ministry gave a death toll of 77 from the violence, mostly demonstrators but also security forces, with some 370 people requiring hospitalization for injuries.
Thousands of opposition supporters remain in central Kyiv’s Independence Square, having withstood strong pressure from security forces this week to vacate the main base of their movement.
In recent days, the EU and the United States both unveiled sanctions targeting Ukrainian officials deemed responsible for the violence.
PHOTO GALLERY: Yulia Tymoshenko
Yulia Tymoshenko walks with her husband, Oleksandr, in Kyiv in 2004.
Yulia Tymoshenko speaks with riot police guarding the presidential-administration building in Kyiv during the Orange Revolution in November 2004.
Orange Revolution leaders Viktor Yushchenko (left) and Yulia Tymoshenko sing the national anthem with supporters during the Orange Revolution in December 2004.
Yulia Tymoshenko's supporters carry her during a massive rally in Kyiv in November 2005 to mark the first anniversary of the Orange Revolution.
Yulia Tymoshenko visits the Kharkiv State Aircraft Manufacturing Company as prime minister in March 2009.
Russian President Vladimir Putin (right) meets with Ukrainian Prime Minister Yulia Tymoshenko (left) and Russian Ambassador to Ukraine Viktor Chernomyrdin at his residence near Moscow in February 2008.
Prime Minister Yulia Tymoshenko and deputies from her bloc submit boxes of documents supporting their allegations of fraud in Ukraine's presidential election to the Supreme Administrative Court in Kyiv in February 2010.
Yulia Tymoshenko, as a leader of the political opposition, speaks with journalists at the parliament building in Kyiv in May 2010.
German Chancellor Angela Merkel (left) is greeted by Ukrainian opposition leader Yulia Tymoshenko after a meeting of the European People's Party in Meise, Belgium, in March 2011.
Activists from the Femen movement wear Tymoshenko costumes during a demonstration in Kyiv in June 2011.
Yulia Tymoshenko sits with her daughter, Yevhenia, and husband, Oleksandr, during a court session in Kyiv in October 2011.
Yulia Tymoshenko (right) addresses the court as Judge Rodion Kireyev reads the verdict against her in Kyiv in October 2011.
Yulia Tymoshenko looks out through a prison window in Kyiv in November 2011.
Yulia Tymoshenko shows bruises from alleged mistreatment in custody in April 2012.
Lithuanian President Dalia Grybauskaite (left) holds the hand of jailed Yulia Tymoshenko during a visit to the Kharkiv hospital where Tymoshenko was being treated in May 2012.
Yevhenia Tymoshenko,Yulia's daughter, attends an exhibition about her mother's case in Paris in June 2012.
Tymoshenko is served with legal papers outlining new accusations against her by Kachanivska Prison Director Ihor Karpaschikov in her hospital room in Kharkiv in January 2013.
Opposition lawmakers in Ukraine's Verkhovna Rada unfurl a banner during a demonstration in support of Tymoshenko in May 2013.
The crisis erupted in November after Yanukovych, under pressure from Russia, declined to sign political and trade accords with the EU that had been under negotiation for years.
After spurning the EU, Yanukovych accepted a $15 billion economic bailout from Russia to help ease Ukraine's crippling debt crisis.
In a development on February 21, Russian Finance Minister Anton Siluanov was quoted as telling Bloomberg News that Moscow has decided to suspend a $2 billion tranche of that aid because of the latest instability in Ukraine.
In his statement, Yanukovych did not accede to the opposition's demand that he resign. However, he described this week's bloodshed as "tragic days," when "people died on both sides of the fence."
He said he was offering concessions because "there is nothing more important than a human life" and that everything must be done to restore peace among Ukrainians.
Crimea Debate Not Held
Elsewhere, Crimea's parliament did not hold an extraordinary session on February 21 to discuss the peninsula's possible separation from Ukraine, as expected.
Media reports on February 20 quoted Crimean parliament speaker Volodymyr Konstantynov as saying Crimea might split from the country if the ongoing antigovernment protests, in which scores have been killed, "ruin Ukraine."
Crimean lawmaker Refat Chubarov had said earlier that parliament would hold a session at midday on February 21 to discuss the issue.
Meanwhile, Crimean Prime Minister Anatolyy Mohylyov said on February 21 that several Crimean supporters of President Viktor Yanukovych were injured by unknown attackers on their way back from Kyiv late on February 20.
Earlier reports said several pro-Yanukovych activists had been killed.
With reporting from Reuters, RT, AFP, AP, UNIAN, and 15minut.org