The Pentagon has denied reports that it approved the transfer of American military equipment for use in a deadly raid on a Russian region bordering Ukraine on Monday. 

Russia alleges that dozens of Ukrainian militants crossed into one of the border towns in its southern Belgorod region, striking targets and forcing an evacuation, before more than 70 of the attackers were killed or pushed back by what the authorities termed a counterterrorism operation.

Shortly after the raid, pictures appeared on social media that appeared to show a number of mostly damaged American-made military vehicles, including an M1224 MaxxPro MRAP armored vehicle, at a border checkpoint crossing. 

On Tuesday a spokesman for the Pentagon, Brigadier General Pat Ryder of the U.S. Air Force, told reporters: “We’ve seen those reports that we obviously continue to monitor very closely.” General Ryder did not address the accuracy of the images. 

“I will say,” he added, “that we can confirm that the U.S. government has not approved any third-party transfers of equipment to paramilitary organizations outside the Ukrainian Armed Forces, nor has the Ukrainian government requested any such transfer. So again, that’s something we will keep a close eye on.”

One group claiming responsibility for the strike, the Russian Volunteer Corps, denied Wednesday it had lost any men and said its action had exposed Russian border weaknesses. The conflicting versions of events reflect the role of disinformation and propaganda in the 15-month war.

Ukraine denied any involvement in the skirmishes Monday and Tuesday. It blamed two Russian groups, including the Russian Volunteer Corps, that claim to be volunteers fighting in coordination with Kyiv’s forces in an uprising against the government of President Putin.

While neither version could be independently verified, whatever happened appears to have sent Moscow scrambling to respond to one of the most serious border incursions since Mr. Putin launched the invasion of Ukraine in February 2022.

Governor Vyacheslav Gladkov of Belgorod said an elderly woman died in the chaotic evacuation, and 12 people were wounded in the attack and shelling.

Two groups — the Russian Volunteer Corps and the Freedom of Russia Legion — claimed responsibility for the attack and announced an ambitious goal of “liberating” the Belgorod region. Little is known about them beyond what they say about themselves.

In early March, the RVC claimed responsibility for an incursion in Russia’s Bryansk region, another border area.

The website of the Freedom of Russia Legion says it was formed last spring “out of Russians’ desire to fight against Putin’s armed gang” and is “officially recognized” by Kyiv’s military. “We are fighting in full cooperation with the Armed Forces of Ukraine and under the leadership of the Ukrainian command,” the website says.

A well-known Russian far-right figure, Denis Nikitin, described himself as commander of the Russian Volunteer Corps when he met reporters Wednesday in Ukraine’s northern Sumy region bordering Russia.

He described the group as “a right-wing, conservative, military, semi-political organization,” saying its fight is against Mr. Putin and his state apparatus.

He declined to say how many soldiers were involved in the Belgorod raid.

Mr. Nikitin said that inside Ukraine, the RVC’s actions are planned with the knowledge and assistance of Ukraine’s military, but anything outside the country’s borders “is our decision.”

The RVC sources its own military equipment, he added.

Ukrainian officials have never confirmed any ties with either group. The government in Kyiv denied involvement in this week’s Belgorod incident, calling it an act by disgruntled Russians.

When they did talk about it, officials were vague. The deputy defense minister, Hanna Maliar, said “patriots of Russia” and “people who actually rebelled against Putin’s regime” were behind the attack. A presidential adviser, Mykhailo Podolyak, blamed “underground guerrilla groups” that are “composed of Russian citizens.”

In remarks to the news outlet Suspilne, a Ukraine intelligence official, Andrii Yusov, said it was the Russian Volunteer Corps and the Freedom of Russia Legion.

Another intelligence representative, Andrii Cherniak, pointed to the fact that the two groups claimed responsibility. “This is the consequence of aggressive politics of Putin’s regime and Russia’s invasion of Ukraine,” he told the Associated Press.

An analyst on the Russian military, Mark Galeotti, told Reuters that “the two groups involved in the fighting in Belgorod are made up of anti-Kremlin Russians ranging from liberals and anarchists to neo-Nazis.” They aspire to the downfall of the Putin regime, he said, but at the same time, “we have to realize that these are not independent forces. … They are controlled by Ukrainian military intelligence.”

Biden administration officials have previously said that Washington does not “enable or encourage” Ukrainian attacks on Russian territory, but unanswered questions about Monday’s raid will raise tensions in the region. 

Russia calls it an incursion by saboteurs deployed by Kyiv, with officials and state media using various epithets ranging from “militants” to “terrorists.”

A defense ministry spokesman, Igor Konashenkov, said more than 70 “Ukrainian terrorists” were killed in Russia’s operation. He also referred to the attackers as “nationalists.”

Russian state TV reported the invaders were from Ukraine’s armed forces. At least one report alleged the attackers used American military equipment despite Washington’s assurances its weapons will not be used for attacks inside Russian territory.