Moscow said Tuesday it had fought off an assault in its Belgorod region after two days of battles with attackers who had staged a cross-border raid.
Much is unclear about the fighting. Russia says the raid was conducted by saboteurs from the Ukrainian military; Ukraine says it was carried out by Russian citizens who rose up independently.
Washington has provided billions of dollars of military assistance to Kyiv, but has sought to restrict its use to the defense of Ukrainian territory, rather than attacks on Russian soil that could potentially be used as a reason for the Kremlin to escalate the conflict.
Video posted by the Russian Defense Ministry and verified by NBC News show American-made Humvees and MRAP armored vehicles at a Russian border checkpoint following the alleged incursion by pro-Ukraine and anti-Putin fighters.
The Russian Volunteer Corps — which says it is made up of Russians fighting on behalf of Ukraine, some of whom have endorsed neo-Nazi ideologies — also posted video Wednesday morning showing it in possession of MRAP vehicles, although it wasn’t clear where it was filmed. The group has claimed to be behind a previous cross-border raid.
Denis Kapustin, its white nationalist leader who has pro-Nazi views, told the Financial Times newspaper that his group was in possession of the American-made vehicles but declined to say how it got them. Kapustin, who also goes by Nikitin, is a well-known skinhead and an ex-soccer hooligan.
Some analysts questioned the appearance of the vehicles in the video shared by the Russian Defense Ministry, pointing to a lack of visible damage and their placement.
“It’s possible the vehicles were used in some form of assault, but it’s also possible the image is staged — a long-standing practice of disinformation employed by the Kremlin to cast a narrative. This narrative conveniently matched the domestic Russian audience narrative that the U.S. and NATO threaten the security of Russia,” said Clint Watts, a national security analyst for NBC News and MSNBC.
Asked about the images, U.S. officials said they were monitoring the reports.
"It’s something we’re keeping a close eye on," Air Force Brig. Gen. Pat Ryder, a Defense Department spokesman. "I don't know if it's true or not, in terms of the veracity of that imagery."
He added that the U.S. has not authorized Ukraine to give this equipment to anyone else, and that Ukraine has not asked for the right to do so.
“We’re skeptical at this time of the veracity of these reports,” State Department spokesman Matthew Miller said.
Both of them stressed that the U.S. does not "encourage or enable strikes inside of Russia," as Miller put it. “But, as we’ve also said,” he added, “it is up to Ukraine to decide how to conduct this war.”
This caveat is part of a wider debate in the West about how much military backing to give Ukraine without provoking a direct war with Russian President Vladimir Putin.
"It is no secret to us that more and more equipment is being supplied" to Ukraine, Kremlin spokesman Dmitry Peskov said in a daily news briefing Wednesday. And "it's no secret that this equipment is used against our military," he said.
Turning his attention to the U.S. and its allies, he added, "It's no secret that the direct and indirect involvement of these Western countries in this conflict is growing every day. We draw the appropriate conclusions."
Half of Americans support the Pentagon's ongoing supply of weapons to Ukraine, according to a survey by the University of Chicago's Harris School of Public Policy and the The Associated Press-NORC Center for Public Affairs Research this week.
If the images of American vehicles are genuine, it's not clear how they came to be used in a battle on Russian soil.
Russian Defense Ministry spokesman Igor Konashenkov said 70 attackers, who he said were saboteurs from the Ukraine military, were killed but did not mention Russian casualties.
Kyiv denies this. Andriy Yusov, a spokesman for Ukraine's military intelligence directorate, told NBC News that the attackers were Russian citizens from the Russian Volunteer Corps and the Freedom of Russia Legion.
The militias "acted completely autonomously," he said, while the Ukrainian army is "engaged solely in the liberation of occupied Ukrainian territories within the internationally recognized borders of Ukraine."
The group said in its Telegram channel that the goal of the operation was to “liberate” the border region, which lies some 45 miles north of the city of Kharkiv in eastern Ukraine and far from the war's front lines.
The huge arsenal provided to Ukraine by its Western backers, including British cruise missiles and American F-16s, comes with the strict requirement that it’s not used to target Russia itself.
“So for Ukraine to pull this off they absolutely have to do it in a deniable fashion through proxies,” said Samuel Ramani, an expert in Russia’s military operations at the University of Oxford.