From 18 February when violence erupted in Kiev to 3 March when Russia gave Ukraine's forces an ultimatum to surrender in Crimea. Here is a chronology of key events in Ukraine as Russia and the West face off.February 18
Violence erupts as 20,000 pro-European protesters rally in Kiev to demand president Viktor Yanukovych be stripped of key powers. Protesters fight riot police on Independence Square, which demonstrators have occupied for three months to protest Yanukovych's decision to reject an EU trade deal in favour of closer ties with Russia.
Police open fire. An official toll lists 82 people killed in three days, including around 15 police. February 22
Parliament impeaches Yanukovych as he flees Kiev condemning a "coup". Presidential elections are set for May 25. Opposition leader Yulia Tymoshenko, who was sentenced to a seven-year jail term in 2011 for abuse of power, is released.
Parliament elects Tymoshenko ally Volodymyr Turchynov as interim president.
Parliament urges the International Criminal Court to prosecute Yanukovych for the "mass murder" of protesters in Kiev.
Russia, which questions the legitimacy of Ukraine's new leadership, 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.
Pro-Russian gunmen seize parliament and government buildings in Simferopol, raising the Russian flag.Parliament approves Tymoshenko ally Arseniy Yatsenyuk as prime minister heading a pro-Western cabinet.
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.
Yanukovych insists he has not been overthrown as he resurfaces at a news conference in Russia.March 1
Putin wins parliament's authorisation to send troops into Ukraine. The Ukrainian army is put on a state of alert.
A referendum to determine whether Crimea residents want greater autonomy is brought forward to March 30.
Obama tells Putin that Moscow has violated international law and warns of reprisals. Putin insists Russia has the right to "protect its interests and Russian-speaking populations".
Yatsenyuk accuses Russia of declaring war.
US Secretary of State John Kerry tells Russia it risks losing its place in the prestigious Group of Eight.
Russian forces are "now in complete operational control of the Crimean peninsula", according to a US official.
Ukraine's navy chief switches allegiance to the pro-Russian authorities of Crimea, a day after he is appointed.March 3
Russian Foreign Minister Sergei Lavrov criticises threats of "sanctions and boycotts" and accuses Ukraine's new leaders of attacking minority rights.
Ukraine accuses Russia of pouring more troops into Crimea. All military bases in Crimea are surrounded, the regional defence ministry says.
Some 300 pro-Russian demonstrators occupy the regional government building in the eastern city of Donetsk, stronghold of Yanukovych.
The Russian parliament speaker says there is no need yet to use Russia's "right" to launch military action in Ukraine.
Advance teams of monitors from the Organisation for Security and Cooperation in Europe (OSCE) to start deploying in Ukraine late Monday.
Moscow's stock markets slump 13 percent, while global markets also sink, and the price of oil surges.
Russia gives Ukraine's forces an ultimatum to surrender in Crimea or face an assault, Ukraine's military says. Russia's Black Sea fleet based in Crimea denies. A US official says any such ultimatum would be a "dangerous escalation".
The EU schedules an emergency summit on Ukraine Thursday.