Here is a chronology of key events in Ukraine as the Russian parliament on Saturday approved a request by Russian President Vladimir Putin to send troops into Ukraine despite Western warnings not to intervene amid rising tensions on the flashpoint Crimean peninsula.
Nov. 21: President Viktor Yanukovych's government announces that it is abandoning an agreement that would strengthen ties with the European Union and instead seeks closer cooperation with Moscow. Protesters take to the streets.
Nov. 30: Police brutally attack a group of protesters, detaining 35. Images of protesters bloodied by police truncheons spread quickly and galvanize public support for the demonstrations. A protest on Dec. 1 attracts around 300,000 people, the largest in Kiev since the Orange Revolution in 2004. Activists seize Kiev City Hall.
Dec. 17: Russian President Vladimir Putin announces that Moscow will buy $15 billion worth of Ukrainian government bonds and allow for a sharp cut in the price Ukrainians pay for Russian natural gas. Putin and Yanukovych claim there are no conditions attached.
Jan. 22: Two protesters die after being hit with live ammunition and the third after a fall during a confrontation between police and demonstrators manning barricades, the first protest deaths.
Jan. 28: The prime minister resigns and parliament repeals the new harsh anti-protest laws that set off the violence of a week earlier. Both are concessions to the opposition aimed at defusing the crisis.
Jan. 31: Opposition activist Dmytro Bulatov, missing since Jan. 22, resurfaces badly bruised and with part of his right ear cut off. He believes a pro-Russia group was behind his kidnapping and torture, raising fears among the opposition that extrajudicial squads are being deployed to intimidate protesters.
Feb. 16: Opposition activists end their occupation of Kiev City Hall in exchange for the release of all 234 jailed protesters, in what is seen as a sign of progress toward resolving the crisis peacefully.
Feb. 18: Violence erupts as 20,000 pro-European protesters rally in Kiev to demand that president Viktor Yanukovych be stripped of key powers.
- Protesters fight riot police on Independence Square, which demonstrators have occupied for three months.
Feb. 20: Police open fire. An official toll lists 82 people killed in three days, including around 15 police.
Feb. 21: The president and opposition leaders, under pressure from European foreign ministers, approve early elections and the formation of a new unity government.
Feb. 22: Parliament speaker Volodymyr Rybak resigns and several deputies quit the ruling Regions Party. Rybak is replaced by Oleksandr Turchynov, an aide for jailed ex-premier Yulia Tymoshenko.
- Yanukovych flees Kiev, but denies he plans to resign and condemns a "coup".
- The parliament votes to hold presidential elections on May 25 and impeaches Yanukovych, saying he "is removing himself (from power) because he is not fulfilling his obligations".
- Tymoshenko, sentenced to a seven-year jail term in 2011 for abuse of power, is released after a vote by parliament.
Feb. 23: Turchynov is elected interim president by parliament.
Feb. 24: Ukraine appeals for $35 billion (25 billion euros) in Western aid to save the country from economic collapse.
- Russia questions the legitimacy of Ukraine's new leadership.
Feb. 25: Parliament urges the International Criminal Court to prosecute Yanukovych for the "mass murder" of protesters in Kiev.
Feb. 26: Putin puts armed forces in the area near Ukraine on high alert.
- Pro-Russian demonstrators brawl with supporters of interim authorities in Simferopol, capital of the Russian-speaking peninsula of Crimea.
- Kiev requests an international arrest warrant for Yanukovych.
- Ukraine's new leaders nominate a pro-Western cabinet led by Tymoshenko ally Arseniy Yatsenyuk.
Feb. 27: Pro-Russian gunmen seize parliament and government buildings in Simferopol, raising the Russian flag.
- Turchynov says any movement of Russian troops out of their Crimean bases "will be considered as military aggression".
- US Vice President Joe Biden promises Ukraine's interim leaders "full" US support.
- Parliament approves Yatsenyuk as prime minister.
Feb. 28: The new authorities in Ukraine say they have regained control of two Crimean airports seized during what the interior minister charged was an "armed invasion" by Russian forces.
- The parliament calls on the United States and Britain to uphold a pact signed with Russia to ensure Ukraine's sovereignty.
- France, Germany and Poland say they are "deeply concerned" about Crimea.
- The central bank imposes a limit of 15,000 hryvna (1,100 euros, $1,400) on bank withdrawals.
- Yanukovych insists he has not been overthrown as he resurfaces at a news conference in Russia near the Ukrainian border. He vows to continue to fight for Ukraine's future.
- Putin calls for a rapid return to normality in Ukraine and warns against any further escalation of unrest, the Kremlin says.
- US Secretary of State John Kerry says Russia is ready to help Ukraine as it seeks to stave off economic collapse.
- US President Barack Obama says he is deeply concerned about reports of Russian military activity in Ukraine and warns of "costs" to any infringement of its sovereignty. A senior US official says Obama could skip the G8 summit in Sochi in June if Moscow's forces are involved in the country.
March 1: The Russian upper house approves a request from Putin to deploy Russian forces in Ukraine. Earlier the body's speaker says Russia could send a "limited contingent" of troops to Crimea to assure the security of Russia's Black Sea Fleet and its citizens.
- Dozens of masked and uniformed gunmen without any insignia take positions next to Crimea's regional parliament building. Ukraine's defence chief accuses Moscow of sending 6,000 troops and 30 armoured personnel carriers to Crimea.
- London says British Foreign Secretary William Hague will visit Kiev on Sunday for talks with the interim Ukrainian government as other Western governments voice concern about developments in Crimea, with Sweden's Foreign Minister Carl Bildt tweeting that the "likely immediate aim is to set up puppet pro-Russian semi-state" there.
- Gazprom says Ukraine owes the Russian gas giant a "huge" debt of $1.55 bn for unpaid gas and may be unable to keep the discount it currently enjoys for Russian gas imports.
- A referendum to determine whether Crimea residents want greater autonomy is brought forward to March 30.
- More than 10,000 people carrying Russian flags protest in the eastern Ukrainian city of Donetsk, a Yanukovych stronghold. Dozens are hurt when a pro-Russia protest in Ukraine's eastern city of Kharkiv turns violent.