Ukraine's spy chief says 'Russia is the only beneficiary' of US intelligence leak

KYIV, Ukraine -- Ukraine's most senior military intelligence official said Russia has the most to gain from the massive leak of U.S. government secrets that has dominated headlines in recent days.

In his first interview since classified documents from the U.S. Department of Defense were leaked online last week, Ukrainian Maj. Gen. Kyrylo Budanov told ABC News in Kyiv on Wednesday evening that information warfare of this kind is nothing new.

"Russia is the only beneficiary of this," Budanov said.

Attorney General Merrick Garland announced Thursday that a member of the Massachusetts Air Force National Guard was arrested by FBI agents in North Dighton, Massachusetts, in connection with the leaked documents probe.

Jack Teixeira, 21, was taken into custody in relation to the investigation into "alleged authorized removal, retention and transmission of classified national defense information," Garland said.

Budanov confirmed he spoke with his U.S. counterparts soon after the leak came to light.

"We have communication with relevant services in the U.S.," he added, "and from literally the first few hours, we started to talk."

The Ukrainian intelligence chief insisted there was "no risk" that the matter would damage the relationship between his war-torn country and the United States. Instead, he downplayed the likely impact the shocking revelations will have on the battlefield, as Ukraine endures a second year of Russia's invasion.

"If there is a problem, it will be solved," he told ABC News. "If there is no problem, even better. This will not be able to affect the real results of the offensive operation."

Budanov, who has been credited with predicting the precise date and time of the Russian invasion, talked up the Ukrainian military's ability to make headway in an upcoming and long-awaited counteroffensive against Russian forces, despite U.S. officials suggesting in private that any prospective gains will likely be more modest than last year's lightning operation that returned huge swathes of territory to Ukrainian government control.

"What will be the results of these actions? I think that, in the near future, everyone will see and feel it," he said.

However, Budanov admitted that the "success of this offensive operation is badly needed" -- not just for Ukrainians but also their allies who are supplying them with funds and ammunition. While he noted that the "taxpayers" of countries supporting Ukraine's defensive, such as the U.S., expect to see results, Budanov said he was not aware of any demands made by Western allies nor that continued support would be conditional on battlefield success.

"Without victories, sooner or later, questions will be asked whether it's worth continuing to support Ukraine," he told ABC News.

Budanov sat down with ABC News in his office in the Ukrainian capital just days after the leaked cables, which was described by analysts as the most serious breach of U.S. intelligence in over a decade. Budanov refused to be drawn in on some of the more explosive claims, including what appears to be evidence that U.S. officials were listening in on internal Ukrainian discussions about striking targets deep within Russia.

Further evidence of U.S. assistance for Ukraine emerged earlier Wednesday. A U.S. official confirmed to ABC News that a small military special operations team based at the U.S. embassy in Kyiv has been providing intelligence assistance to Ukrainian special forces and security assistance to VIPs since the early phase of Russia's war. A former U.S. official told ABC News that, in addition to providing assistance with the oversight of U.S. equipment and supplies being sent to Ukraine, they have also assisted Ukrainian military planners with their operations that have resulted in hundreds -- if not thousands -- of Russian military casualties. The sources stressed that they were not in combat.

When talking about Russia, Budanov was characteristically bullish. He made headlines last year when he told ABC News that the Ukrainian military would strike at targets "deeper and deeper" inside Russian territory.

Speaking to ABC News on Wednesday evening, Budanov vowed to take back the Crimean Peninsula and mocked Russian President Vladimir Putin's not-so-veiled nuclear threats and failed "winter offensive," the latter of which has seen minimal gains and heavy losses. While studying a map of Russia, Budanov predicted seismic change within the neighboring country that he believes will play a part in ending Putin's war in Ukraine's favor.

"Borders can be changed," he said. "This is an artificially created mistake and, now, the moment has come for this country to collapse."

ABC News' Luis Martinez, Fidel Pavlenko and Natalia Popova contributed to this report