Ukrainian President Volodymyr Zelenskyy expressed his gratitude Monday to the team of the Oscar-winning film Sunday “20 Days in Mariupol,” on the early horrors of Russia’s invasion of Ukraine in 2022.

In a post on X, formerly Twitter, Zelenskyy said that the coveted award in the Best Documentary category is important for “our entire country.”

“The horrors of Mariupol must never be forgotten. The entire world must see and remember what the inhumane Russian invasion brought to our people,” he wrote.

“Cities and villages were destroyed, homes were burned, and entire families were killed by Russian shells and buried in their own backyards. We still do not know entirely how many people died in Mariupol. However, satellite images show graveyards around the city with thousands and thousands of graves,” Zelenskyy added.

Directed by Ukrainian filmmaker Mstyslav Chernov, the documentary chronicles Russia’s brutal attack and relentless bombardment of the southern port city of Mariupol in the first days of Russia’s invasion of Ukraine in 2022.

The film, Zelenskyy said, “depicts the truth about Russian terrorism."

After nearly a decade covering international conflicts, including the Russia-Ukraine war for The Associated Press, Chernov’s first feature film is a harrowing first-person account. A joint production of The Associated Press and PBS’s “Frontline,” the film follows Chernov, photographer Evgeniy Maloletka and producer Vasilisa Stepanenko as they record from inside the besieged city.

The team arrived there an hour before Russia began bombing. Two weeks later, they were the last journalists there working for an international outlet, sending crucial dispatches to the outside world showing civilian casualties of all ages, the digging of mass graves, the bombing of a maternity hospital and the sheer extent of the devastation.

“We were reporting inside the hospital when gunmen began stalking the corridors. Surgeons gave us white scrubs to wear as camouflage,” Chernov said.

Ukrainian-born Chernov narrated the documentary. He and his team won the 2023 Pulitzer Prize for public service.

While accepting the Academy Award, an emotional Chernov said, “This is the first Oscar in Ukrainian history, and I’m honored.” He continued, “probably I will be the first director on this stage to say I wish I’d never made this film, I wish to be able to exchange this to Russia never attacking Ukraine.”

He called on Russia to cease aggression in Ukraine. “I wish for them to release all the hostages, all the soldiers who are protecting their land, all the civilians who are in their jails,” he said.

The city of Mariupol, on the Sea of Azov, was almost completely destroyed by Russian attacks that Kyiv says killed tens of thousands of civilians.

The award comes as the Ukrainian army is struggling to repel Russian forces on the front lines and a $60 billion U.S. aid package is being stalled by political wrangling in Congress.

“This documentary serves as a reminder of why international assistance — without delays or interruptions — is so critical to Ukraine,” Zelenskyy said on X. “The Russian evil does not pause and does not seek peace. They want to inflict the same fate on every city that they can reach as they did on Mariupol, Bucha, and our other cities that suffered under Russian occupation. Together, we must prevent Russia from destroying life.”

Zelenskyy thanked everyone who is telling the truth about Russia's war crimes.

When asked about the film’s success, the Kremlin declined to comment. Russia has denied targeting civilians in Ukraine.

Some information is from The Associated Press, Agence France-Presse and Reuters.