Members of the Ukrainian forces participate in a combat training exercise. (Ethan Swope/Bloomberg via Getty Images)

WASHINGTON: Russian forces have officially begun attacks inside Ukraine, setting off a long-feared conflict that in recent weeks began to feel inevitable.

Just before 5 am Kyiv time, Russian President Vladimir Putin released a video declaring a “special military operation” to “demilitarize” Ukraine. Immediately after, media reports started coming in of explosions in Kyiv. Russian authorities had earlier closed the airspace along the Russian-Ukraine border to civilian air traffic.

Russia is expected to bring an overwhelming military force against its former Soviet vassal. American intelligence leaks have indicated a belief that the Russian forces will head towards the capitol city of Kyiv, in an attempt to take control as quickly as possible. Civilian casualties are expected to be high.

RELATED: In 2021, Breaking Defense’s Kyiv correspondent wrote an explainer of Putin’s history with Ukraine. Read it here.

Late last month Chairman of the Joint Chiefs Gen. Mark Milley painted a dire picture of what would happen in the event of an invasion.

“Given the type of forces that are arrayed, the ground maneuver forces, the artillery, the ballistic missiles, the air forces, all of it packaged together, if that was unleashed on Ukraine, it would be significant… and it would result in a significant amount of casualties,” Milley said on Jan. 28. “And you can imagine what that might look like in dense urban areas, all along roads, and so on and so forth. It would be horrific.”

In a statement Wednesday night, US President Joe Biden said the “prayers of the entire world are with the people of Ukraine tonight as they suffer an unprovoked and unjustified attack by Russian military forces. President Putin has chosen a premeditated war that will bring a catastrophic loss of life and human suffering.

“Russia alone is responsible for the death and destruction this attack will bring, and the United States and its Allies and partners will respond in a united and decisive way. The world will hold Russia accountable.”

On Monday, Putin capped off an extraordinary, almost hour-long speech in which he called into question the very concept of a Ukrainian nation by signing a declaration officially recognizing the self-proclaimed breakaway republics of Donetsk and Lugansk. That was followed up by an order from Putin to conduct “peacekeeping” activities in the two Ukrainian territories, which have been the site of an eight-year long conflict since Russia’s seizure of Crimea in 2014.

By Wednesday, the leaders of those two factions issued a request for help from Russia. Russian forces, including tanks, were captured on social media heading deeper into Ukrainian territory, beyond the areas held by pro-Russian militias for much of the last eight years.

Over the last two months Breaking Defense has published a number of stories and opinion pieces about the Ukrainian situation. Here is a selection:

This is a developing story and may be updated.