Russia-Ukraine updates: Putin says war was ‘unleashed’ on Russia

As tens of thousands of Russian troops lined up along Ukraine’s eastern and northern borders for "military exercises" last February, some international observers warned that Russia was about to do the unthinkable.

U.S. President Joe Biden had declassified intelligence in the weeks prior that showed an attack on Ukraine's sovereignty was imminent. That intel was shared with allies, in an attempt to rally support and to stop the war, but the effort proved unsuccessful. The invasion began on Feb. 24, 2022.

The following four seasons have seen some of the bloodiest fighting on European soil in generations. Tens of thousands of Russian and Ukrainian troops have been killed. And Ukrainian civilians have been terrorized by missiles aimed at energy infrastructure, city centers and apartment buildings.

This month marks both the 9-year anniversary of Russian President Vladimir Putin's invasion of Ukraine's Crimean Peninsula, which he illegally annexed in 2014, and the first anniversary of his full-scale invasion of Ukraine.

The ends to which he'd go in his mission to capture Ukraine have become clear in the last year.

-ABC News' Kevin Shalvey

There was a somber mood over Kyiv on Friday morning as the country marks the one-year anniversary of Russia's full-scale invasion while bracing for a potential barrage of missile strikes.

Ukrainian President Volodymyr Zelenskyy, along with the country's top general and the defense minister, took part in a military ceremony in Sofia Square in the historical center of the capital city. Zelenskyy and Poland's president also visited a memorial wall for fallen Ukrainian soldiers.

Ukrainians are anticipating Russian missile strikes to mark the anniversary, amid warnings from the Ukrainian Air Force that there is a high risk of them. But so far it has been quiet, with no major strikes beyond routine shelling in northern and eastern Ukraine.

-ABC News' Patrick Reevell

Russian President Vladimir Putin announced on Feb. 21, 2022, that he had recognized two Russian-backed separatist areas in eastern Ukraine, Donetsk and Luhansk, as independent states.

Ukrainian President Volodymyr Zelenskyy followed the announcement by saying that Ukraine had cut diplomatic ties with Russia. Putin then gave a speech on Feb. 24, 2022, announcing he would launch a "special military operation" in Ukraine.

Minutes after the announcement, explosions could be heard in Kyiv. What followed was a full-scale invasion of Ukraine, with thousands of troops crossing the country's borders. Here are the key events that occurred in the year since then.

-ABC News' Nadine El-Bawab