KYIV — Washington is investigating reports that U.S. military vehicles were used in raids on Russia, a White House official said Wednesday, warning Ukraine and pro-Ukraine forces against using U.S. equipment to attack inside Russia.

Two pro-Ukraine Russian paramilitary groups claimed responsibility for an incursion Monday into Russia’s Belgorod region from Ukraine, in which they overran several small villages. Moscow said Wednesday it had defeated the groups, killing more than 70 people and destroying U.S.-made military vehicles.

U.S. National Security Council spokesperson John Kirby said Wednesday the White House is “looking into those reports that the U.S. equipment and vehicles could have been involved,” hinting at frustration in Washington.

“We’ve been pretty darn clear: We don’t support the use of U.S.-made equipment for attacks inside Russia … we’ve been clear about that with the Ukrainians,” Kirby said. “I won’t get into private discussions that we’re having with them. But I think we’ve been nothing but consistent about our concerns in that regard.”

Pentagon spokesperson Brig. Gen. Patrick Ryder on Tuesday said the U.S. had not authorized nor received Ukrainian requests for transferring equipment to paramilitary groups. He also expressed doubts about the Russian reports and images appearing to show U.S.-made vehicles. 

“I don’t know if it’s true or not, in terms of the veracity of that imagery,” said Ryder. “You’ll recall [this week] there were some bogus images of reported, alleged explosions at the Pentagon. So, you know, we just — all of us, both within the [defense department] and I’m sure in the … journalistic community, have to take a look at these things and make sure we get the facts before we make assumptions.”

Ukraine has denied involvement in the attack, saying the two groups — Legion of Free Russia and Russian Volunteer Corps — consist only of Russian citizens who are fighting on Kyiv’s side, aiming to create a demilitarized zone on the border with Ukraine.

Andriy Cherniak, a representative of Ukraine’s Military Intelligence or HUR, told POLITICO that military aid provided by the U.S. and other Western allies is strictly limited for use by the Ukrainian army.

“Every bullet is tracked not only by us but also by our Western allies,” Cherniak said, adding he did not know where the paramilitary groups got the U.S.-made vehicles. While he insisted the groups acted on their own, Cherniak said HUR has been in contact with them and has observed increased anti-Putin sentiment among Russians.

“Our main goal is to protect Ukraine. For us, those are Russian citizens who are against Putin and want to shake his regime. So we work with whoever we can to reach our main goal,” Cherniak said. “More and more in Russia understand they don’t want to die for [Putin] at war.”

Russian Defense Minister Sergei Shoigu described the groups as Ukrainian “nationalists” during a televised meeting with Russian military officials and displayed images of two severely damaged armored vehicles that look similar to those provided by the U.S. to Ukraine as part of military aid.

“During counterterrorist operations, units of nationalist formations were blocked and defeated by air strikes and artillery fire and active actions. The remnants of the nationalists were thrown into the territory of Ukraine, where the fight continued until they were completely eliminated,” Shoigu said.

The two groups themselves, however, claimed they were able to return to Ukraine with only two killed and 10 injured from the Legion of Free Russia, as well as two injured from the Russian Volunteer Corps.

When asked about how they got U.S.-made vehicles, Russian Volunteer Corps’ Denis Kapustin, aka “White Rex” (the same name as his white nationalist clothing line), joked that his fighters could have purchased them at any military store — mocking remarks from Vladimir Putin about how Russian-backed militants got weapons to fight Ukraine in Donbas in 2014.

Kapustin also claimed his group had taken back military vehicles stolen from Ukraine.

“The goal of our peacekeeping operation into Belgorod region was also to destroy law enforcement serving Putin’s regime and also demonstrate to the people of Russia that resistance is possible,” the Legion of Free Russia said Tuesday.

The Russian Volunteer Corps also claimed they wanted to show Russians they are not protected by Putin. 

Alexander Ward reported from and Lara Seligman contributed reporting from Washington.