Russia invaded Ukraine in the early hours of February 24, setting off the worst conflict in Europe in decades.

As Russia extends its grip over the east, we look back on 100 days of fighting that has killed tens of thousands of civilians and reduced entire cities to rubble.

Russian President Vladimir Putin announces a "special military operation" to "demilitarise" and "de-Nazify" the former Soviet state and protect Russian speakers there.

A full-scale invasion starts with air and missile strikes on several cities. Ukrainian President Volodymyr Zelensky pledges to stay in Kyiv to lead the resistance.

The West adopts unprecedented sanctions against Russia and offers Ukraine military aid.

Air spaces are closed to Russian aircraft and Russia is kicked out of sporting and cultural events.

Putin puts Russia's nuclear forces on high alert, in what is seen as a warning to the West not to intervene in Ukraine.

During the first peace talks between Kyiv and Moscow, Russia demands recognition of its sovereignty over Crimea, the "demilitarisation" and "de-Nazification" of Ukraine and a guarantee Ukraine will never join NATO. Ukraine demands a complete Russian withdrawal.

Russian troops attack Ukraine's south coast to try to link up territory held by pro-Moscow rebels in eastern Ukraine with the Russian-annexed Crimea peninsula.

On March 3, Kherson in the south becomes the first city to fall. Russian forces relentlessly shell the port of Mariupol.

Russia passes a law punishing what it calls "fake news" about its offensive -- such as referring to its "special military operation" as an invasion -- with up to 15 years in prison.

Russian air strikes raze a Mariupol theatre killing an estimated 300 people sheltering inside. Moscow blames the attack on Ukraine's nationalist Azov battalion.

Zelensky tells the US Congress to "remember Pearl Harbor" and lobbies Western parliaments for more help.

After a month of fighting, Russia withdraws from northern Ukraine, announcing it will focus its efforts on conquering the eastern Donbas region.

On April 2 and 3, Ukrainians find dozens of corpses of civilians scattered on the street or buried in shallow graves in the Kyiv suburb of Bucha, which Russian forces had occupied.

The Ukrainian government has said it believes tens of thousands of people have been killed in Mariupol
The Ukrainian government has said it believes tens of thousands of people have been killed in Mariupol AFP / Alexander NEMENOV

Moscow dismisses accusations of Russian war crimes, saying the images of the bodies are fakes.

A rocket attack on a train station in the eastern city of Kramatorsk kills at least 57 civilians being evacuated from Donbas.

Biden accuses Russia of "genocide", saying Putin appears intent on "trying to wipe out the idea of even being able to be a Ukrainian".

Ukrainian missiles hit and sink Russia's missile cruiser Moskva in the Black Sea, a major setback for Moscow.

US lawmakers back a huge $40-billion package of military, economic and humanitarian aid for Ukraine.

Ukraine says its troops have driven Russian forces back from the outskirts of the country's second-largest city, Kharkiv, to the Russian border.

Finland and Sweden apply to join NATO, reversing decades of military non-alignment because of Russia's invasion of Ukraine.

A Ukrainian court finds a 21-year-old Russian soldier guilty of war crimes and hands down a life sentence for shooting dead a 62-year-old civilian in northeastern Ukraine in the opening days of the war. He has appealed.

Russia declares it is in full control of Mariupol after Ukraine ordered troops holding out for weeks in the Azovstal steelworks to lay down their arms to save their lives.

Nearly 2,500 soldiers surrender and are taken prisoner by Russia.

EU leaders overcome resistance from Hungary to agree a partial ban on most Russian oil imports as part of a sixth wave of sanctions.

The deal bans oil imports delivered by tanker but allows landlocked countries such as Hungary to continue receiving Russian oil by pipeline.

Russian troops seize part of the key eastern Ukrainian city of Severodonetsk, its governor says.

Taking the city would give Russia de-facto control over Lugansk, one of two regions that make up the Donbas, Ukraine's industrial heartland.