Expect more strikes 'deeper and deeper' into Russia, Ukraine’s spy chief tells ABC News

There will likely be further strikes into Russian territory, Ukraine's military intelligence head, Kyrylo Budanov, told ABC News in an interview from Kyiv, without specifically saying whether Ukraine would be behind them.

Ukraine has not claimed responsibility for the Dec. 26 attack on Russia's Engels Air Force Base, which is located more than 800 miles from the Ukrainian border, but Budanov admitted he was "glad to see it."

He added the attacks would come "deeper and deeper" inside of Russia, but would only be able to comment on his country's responsibility for the attacks after the war was over.

And when asked about attacks on Crimea, which was illegally annexed by Russia in 2014, Budanov said, "Crimea is Ukrainian territory, we can use any weapon on our territory."

In late December, Budanov made a public appearance in Bakhmut in Donetsk, the hottest point of the 800-mile front line. What he saw shocked him.

"Soldiers showed me a section where dead bodies are piled up like something you would see in a movie," he said.

"There are hundreds of dead bodies just rotting away in the open field, in places they are piled on top of other bodies like makeshift walls, when Russian troops attack on that field they use those bodies for cover, like a shield," he continued. "But it's not working. There are actual fields of dead bodies there."

Budanov said Russia's weaponry is depleting, forcing it to resort to "cheaper," more "plentiful" solutions, like the Iranian-made, self-destroying Shahed drones, which have sowed fear and panic in the population.

Tehran denies supplying drones to Russia, though the U.S. Department of Defense said Russia has bought hundreds of them.

Russia fired 84 drones at Ukraine in the first two days of 2023, all of which were shot down by Ukrainian air defenses.

The U.S. announced it would supply a Patriot missile defense system to Ukraine in late December, bringing the Biden administration's total military aid for Ukraine close to $22 billion. President Joe Biden recently signed a $1.7 trillion government funding bill that includes $47 billion of additional aid for Ukraine.

"I want to express gratitude for all the help we had, and ask to continue to support Ukraine," said Budanov, telling U.S citizens, "I promise it will not take too long now, and every taxpayer in the U.S. will be able to see where every cent went. We will change this world together."

Budanov also said they are expecting U.S. Bradley Armored Fighting vehicles to be sent to Ukraine soon: "We are waiting for them. We're looking forward to them very much. This will significantly improve the combat ability of our units."

Budanov said he expects fighting to be the "hottest" in March, adding that Ukraine is planning a major push in the spring.

"This is [when we will see more] liberation of territories and dealing the final defeats to the Russian Federation," he said. "This will happen throughout Ukraine, from Crimea to the Donbas."

The Ukrainian leadership has repeatedly said it will not give up an inch of territory.

"Our goal, and we will achieve it, is returning to the borders of 1991, like Ukraine is recognized by all subjects of international law," said Budanov.

As for the future of Russia, Budanov said there are several scenarios in play, but the message is clear: "You should not be afraid of the transformation of Russia. It will only benefit the whole world."

Putin's regime "is a laughingstock for everyone," Budanov said, adding the Russian troops are all but reduced to defending territories they still occupy within Ukraine -- "and not for much longer."

"Russia is not a military threat to the world anymore, just a tall tale," he added.

The only issue remaining, Budanov said, is Russia's nuclear arsenal "and the uncontrollable regime" that will lead "the whole world to realize the necessity of Russia's denuclearization or at least an international overseeing of its nuclear arsenal."

"A terrorist country swinging a nuclear bat at everyone and spewing threats is not a regime that has an ethical or political right to be in control of weapons of mass destruction," Budanov added.

Moments after the interview ended, Budanov warned our team that rockets had been fired at Kyiv from the Black Sea. Hours later, Russia unleashed another massive aerial attack against Ukraine -- ringing in 2023 with terror.

ABC News' Edward Szekeres contributed to this report.