(Reuters) - Russia's invasion of Ukraine enters its 100th day on Friday with no end in sight to the fighting that has killed thousands, uprooted millions and reduced cities to rubble.
After abandoning its assault on the capital, Kyiv, Russia is pressing on in the east and south in the face of mounting sanctions and a fierce Ukrainian counter-offensive bolstered by Western arms.
Some key events in the conflict so far:
* Feb. 24: Russia invades Ukraine from three fronts in the biggest assault on a European state since World War Two. Tens of thousands flee.
* Russian President Vladimir Putin announces a "special military operation" to demilitarise and "denazify" Ukraine. Ukrainian President Volodymyr Zelenskiy tweets: "Russia has embarked on a path of evil, but Ukraine is defending itself."
* Feb. 25: Ukrainian forces battle Russian invaders in the north, east and south. Artillery pounds Kyiv and its suburbs.
* March 1: A U.S. official says a miles-long Russian armoured column bearing down on Kyiv is beset by logistical problems.
* Russia hits a TV tower in Kyiv and intensifies its long-range bombardment of Kharkiv in the northeast and other cities, in what is seen as a shift in Moscow's tactics as its hopes of a quick charge on the capital fade.
* March 2: Russian forces start a siege of the southeastern port of Mariupol, seen as vital to Moscow's attempts to link the eastern Donbas region with Crimea, the Black Sea peninsula Russia seized in 2014.
* Russian troops enter the Black Sea port of Kherson, the first large urban centre captured.
* One million people have fled Ukraine, the U.N. refugee agency (UNHCR) says.
* March 4: Russian forces seize Zaporizhzhia nuclear power plant, Europe's biggest. NATO rejects Ukraine's appeal for no-fly zones, saying they would escalate the conflict.
* March 8: Civilians flee the northeastern city of Sumy in the first successful humanitarian corridor agreed. Two million have now fled Ukraine, the UNHCR says. * March 9: Ukraine accuses Russia of bombing a maternity hospital in Mariupol, burying people in the rubble. Russia says Ukrainian fighters were occupying the building.
* March 13: Russia extends its war deep into western Ukraine, firing missiles at a base near the border with NATO member Poland.
* March 16: Ukraine accuses Russia of bombing a Mariupol theatre where hundreds of civilians are sheltering. Moscow denies it.
* March 25: Moscow signals a shift in focus to making gains in the east, while Ukrainian forces press to recapture towns outside Kyiv.
* March 30: More than 4 million people have fled Ukraine, the UNHCR says.
* April 3/4: Ukraine accuses Russia of war crimes after a mass grave and bodies of people shot at close range are found in the recaptured town of Bucha. The Kremlin denies responsibility and says images of bodies were staged.
* April 8: Ukraine blames Russia for a missile attack on a train station in Kramatorsk that killed at least 52 people trying to flee the looming eastern offensive. Moscow denies responsibility.
* April 14: Russia's lead warship in the Black Sea, the Moskva, sinks after what Ukraine says was a missile strike. Russia blames an ammunition explosion. * April 18: Russia launches what Ukraine describes as the Battle of Donbas, a campaign to seize two provinces and salvage a battlefield victory. * April 21: Putin declares Mariupol "liberated" after nearly two months of siege, but hundreds of defenders hold out inside the city's huge Azovstal steelworks.
* April 25/26: Moldova's pro-Russian breakaway region of Transdniestria says blasts hit a ministry and two radio masts. It blames neighbouring Ukraine. Kyiv accuses Moscow of staging the attacks to try to widen the conflict.
* April 28: Russia fires two missiles into Kyiv during a visit by U.N. Secretary-General Antonio Guterres, Ukraine says. The Kremlin accuses Ukraine of attacking Russian regions near the border.
* May 1: About 100 Ukrainian civilians are evacuated from Mariupol's ruined Azovstal steelworks, in what the United Nations says is a "safe passage operation".
* May 7: As many as 60 people are feared dead after a bomb strikes a village school in Bilohorivka, eastern Ukraine, the regional governor says.
* May 9: Putin exhorts Russians to battle in a defiant Victory Day speech, but is silent about plans for any escalation in Ukraine.
* May 10: Ukraine says its forces have recaptured villages north and northeast of Kharkiv in a counter-offensive. * May 12: More than 6 million people have fled Ukraine, the UNHCR says.
* May 14: Ukrainian forces have launched a counteroffensive near the eastern Russian-held town of Izium, the local governor says.
* May 18: Finland and Sweden apply to join NATO, a move that would lead to the expansion of the Western military alliance that Putin aimed to prevent.
* May 20: Russia says the last of Ukrainian fighters holding out at Mariupol's Azovstal steelworks have surrendered. Hours earlier, Zelenskiy said Ukraine's military had told the defenders they could get out and save their lives.
* May 21/22: Russia launches an offensive in Luhansk, one of two provinces in Donbas, focusing the attack on twin cities of Sloviansk and Sievierodonetsk.
* May 23: In the first war crimes trial of the conflict, a Kyiv court sentences a young Russian tank commander to life in prison for killing an unarmed civilian.
* May 25: Putin signs a decree simplifying the process for residents of newly captured districts to acquire Russian citizenship and passports in a bid to solidify Moscow's grip on the seized territory.
* May 29: Russia's Foreign Minister Sergei Lavrov calls the "liberation" of Donbas an "unconditional priority" for Moscow, while Russian forces appear close to seizing the entire Luhansk region there after days of slow but steady gains.
* May 31: Local officials say it is no longer possible to evacuate civilians trapped in Sievierodonetsk, where Ukrainian forces are still holding out but much of the city is under Russian control.
* June 1: Russia criticises U.S. decision to supply advanced rocket systems to Ukraine, warning it could widen the conflict and increase the risk of direct confrontation with Washington. Secretary of State Antony Blinken says Ukraine had given assurances it will not use the systems against targets on Russian territory.
(Compiled by Andrew Heavens and Tomasz Janowski; Editing by Alison Williams)