WATCH: Pentagon press secretary John Kirby holds a news briefing

As the Russian offensive in eastern Ukraine begins to unfold, the Pentagon said 18 U.S. howitzers to bolster Ukraine’s defense will be transported “very soon.”

Watch Kirby’s remarks in the player above.

“We’ve definitely sourced the 18,” said Pentagon spokesman John Kirby.

“We know where they’re coming from. It’s really just a matter now of getting them packaged up and getting them on the way,” Kirby said.Kirby predicted they would arrive in Ukraine in “a matter of days.”

The U.S. military’s assessment of Russia’s renewed offensive in eastern Ukraine is that it has begun in a limited way, mainly in an area southwest of the city of Donetsk and south of Izyum.

The U.S. estimates that the Russian military has lost about 25 percent of the combat power it sent into Ukraine at the start of the war, so they’re refitting ground combat units for insertion into Ukraine.

A Pentagon official said the Russians added two more battalion tactical groups in the past 24 hours, for a total of 78. That’s up from 65 last week.

“Mr. Putin still has a lot of his inventory available to him,” Kirby said.

“Some of it’s been depleted, some of it’s been destroyed. Some of it’s been captured. But he still has a lot of combat capability available to him.”

Kirby said the Pentagon has no indication that any Western military equipment has been “hit or deterred” Moscow.

He also said the U.S. believes that not all Russian sailors aboard Moscow’s Black Sea flagship “Moskva” survived when it was struck by two Ukrainian missiles several days ago.

“How they perished, how many perished, we just don’t know,” he said.