PHOTOS | Russia's invasion of Ukraine: the most shocking images of the balance of the war

Editor's Note: This gallery contains disturbing images.

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After months of military preparation and troop buildup, Russia launched an unprecedented attack on Ukraine in late February 2022.

Explosions echoed through several Ukrainian cities, including the capital Kyiv, in a wide-ranging invasion that began before dawn on February 24.

Fighting continues across the country and so far the Ukrainian resistance has been able to hold kyiv and many other key cities.

Meanwhile, more than 4.5 million refugees have fled Ukraine to neighboring countries, according to the United Nations refugee agency.

The United States, the European Union and other Western allies have been implementing sanctions in response to Russia's actions.

Many people around the world have also rallied in support of Ukraine.

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Russia had been tightening its military grip on Ukraine since last year, amassing tens of thousands of troops, as well as equipment and artillery, on its neighbor's doorstep.

The escalation in the multi-year conflict has triggered Europe's biggest security crisis since the Cold War, and has also sparked an intense standoff between Western powers and Moscow.

Emergency workers remove the body of a person killed during the Russian attack on the city of Mariupol, Ukraine, on April 21.

Vova, 10, looks at the body of her mother, Maryna, lying in a coffin as her father, Ivan, prays during her funeral in Bucha, Ukraine, on April 20.

Maryna died during the Russian occupation, while the family took refuge in a cold basement where they spent more than a month.

Ukrainian President Volodymyr Zelensky, right, speaks with European Council President Charles Michel during a meeting in Kyiv, Ukraine, on April 20.

A group of firefighters work in Lviv, Ukraine, after a civilian building was hit by a Russian missile on Monday, April 18.

There were at least four missile attacks reported in Lviv and at least seven deaths.

Smoke rises over Mariupol, Ukraine, on April 18.

Ukrainian forces besieged in Mariupol have rejected Russian demands to surrender and are still resisting a relentless assault on the southeastern port city, senior Ukrainian officials said on Sunday, April 17.

The city has been surrounded by Russian troops since March 1.

Women clean the interior of a destroyed building at the military-industrial complex of the Vizar company in Vyshneve, Ukraine, on Friday, April 15.

The site outside Kyiv was attacked by Russian troops.

Firefighters work on a burning building in Kharkiv following a missile attack near the city's International Airport on Tuesday, April 12.

Mourners react in Stebnyk, Ukraine, during the funeral ceremony for Ukrainian military officer Roman Tiaka.

Tiaka was 47 years old.

Ukrainian forces fire rockets at Russian positions in Ukraine's Donbas region on April 10.

Fighting has intensified in the east of the country.

A man deposits flowers at a train station in Kramatorsk, Ukraine, on April 9.

At least 50 people were killed after Russian forces launched a missile attack on the train station, local officials said.

They said the station was being used by civilians trying to flee the fighting.

A man works to catalog some of the bodies of civilians who died in and around Bucha.

Shocking images showing the bodies of civilians strewn across the Kyiv suburb sparked international outrage and added urgency to ongoing investigations into alleged war crimes by Russia.

Ukrainian President Volodymyr Zelensky has called on Russian leaders to account for the actions of the nation's armed forces.

The Russian Defense Ministry, without evidence, claimed that Bucha's images were "fake".

Search and rescue teams clear rubble after the Ukrainian military regained control of Borodianka, Ukraine, on April 6.

People wait to board a train as they flee Kramatorsk on April 5.

This image shows the destruction at Borodianka on April 5.

The city was home to 13,000 people before the war, but most fled after the Russian invasion.

What remained of the city, after heavy bombing and devastating air strikes, was occupied by Russian forces.

President Volodymyr Zelensky speaks to the media about the atrocities in Bucha on April 4. "It is very difficult to negotiate when you see what (the Russians) have done here," Zelensky emphasized while in the city, surrounded by security.

Anna Zhelisko touches the coffin of her grandson, Ukrainian soldier Dmitry Zhelisko, as she arrives for his funeral in Chervonohrad, Ukraine, on April 3.

She died fighting the Russian army near the city of Kharkiv.

Smoke rises over Odessa, Ukraine, on April 3.

The Russian Defense Ministry confirmed an attack on an oil refinery and fuel storage facility in the port city.

Bodies lie in a street in Bucha on April 2.

Images captured by Agence France-Presse showed at least 20 civilian men killed.

A Ukrainian serviceman stands next to a handcuffed Russian soldier in Kharkiv on March 31.

(Credit: Fadel Senna/AFP/Getty Images)

A satellite image shows a bombed-out warehouse being used by the Red Cross in Mariupol on March 29.

Russian and Ukrainian delegations meet in Istanbul for talks on March 29.

Russia said it would "drastically reduce" its military assault on the Ukrainian cities of Kyiv and Chernihiv.

The announcement came after Ukrainian and Western intelligence assessments recently suggested that Russia's advance on Kyiv was stalling.

The talks also covered other important topics, including the future of the eastern Donbas region, the fate of Crimea, a broad alliance of security guarantors and a possible meeting between Presidents Putin and Zelensky.

A woman named Julia cries alongside her 6-year-old daughter, Veronika, as she speaks to the press in Brovary, Ukraine, on March 29.

The regional government headquarters in Mikolayv, Ukraine, was destroyed following a Russian attack on March 29.

At least nine people were killed, according to the Telegram channel of the Mykolaiv regional media office on March 28.

An armored convoy of pro-Russian troops travels along a road leading to Mariupol on March 28.

A volunteer knits a bulletproof vest in Zaporizhzhia, Ukraine, on March 28.

A woman lights a candle during Sunday service at a monastery in Odessa on March 27.

A Ukrainian serviceman stands in a destroyed building in Stoyanka, Ukraine, on March 27.

A man retrieves items from a burning store after a Russian attack in Kharkiv on March 25.

(Credit: Felipe Dana/AP)