Pro-Ukraine fighters appeared to use at least three U.S. military vehicles as they attacked Russian territory on Monday, according to a new report that undermines promises from the Pentagon that U.S. military equipment will only be used within Ukraine's borders.

Russian forces captured at least two American Mine-Resistant Ambush Protected (MRAP) trucks, according to photos confirmed by The New York Times. The equipment was reportedly used by pro-Ukraine proxy forces, which often include Russians who oppose Russian President Vladimir Putin. It is unclear how these pro-Ukraine forces may have obtained U.S. military equipment.

Brig. Gen. Pat Ryder, the Pentagon press secretary, said Tuesday in response to the report that the U.S. government has not approved any decision by Ukraine to transfer U.S. military equipment to third-party forces in the war. He said the Pentagon is looking into the specific incident in Russia to see if the photos of the MRAPs can be confirmed.

ANTI-PUTIN GROUPS CLAIM RESPONSIBILITY FOR BELGOROD ATTACK IN RUSSIA

Russia military vehicles near Mariupol, Ukraine

Russian military vehicles move on a highway in an area controlled by Russian-backed separatist forces near Mariupol, Ukraine, in late April. (AP/Alexei Alexandrov)

"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 transfers," Ryder said. "It's something we'll keep a close eye on."

The Biden administration has emphasized that U.S. military aid to Ukraine would only be used within the country's borders as it defends against Russian attacks.

"The Ukrainians have given us assurances that they will not use these systems against targets on Russian territory," Secretary of State Antony Blinken said in June.

BIDEN CONCESSION ON MILITARY JETS IS HIS LATEST SHIFT TOWARD HEAVILY ARMING UKRAINE

Brig. Gen. Patrick Ryder

Brig. Gen. Pat Ryder, the Pentagon press secretary, said Tuesday in response to the report that the U.S. government has not approved Ukraine to transfer U.S. military equipment to third-party forces in the war. (AP Photo/Andrew Harnik)

Former intelligence officer Rebekah Koffler said this promise is not only impossible to keep, but likely intended to be broken, as the intelligence community hopes to weaken Putin's influence.

"We’re saying to the rest of the world: it’s our policy we won't let them do that," Koffler said of U.S. military equipment in Russia. "But in reality, we want them to do that."

One obvious reason to suspect this, Koffler said, is that the U.S. itself used proxies to dodge blame in its own wars in the Middle East.

"You can’t control what Ukraine is going to do with this weaponry," she said. "You certainly can’t control what the proxy forces are going to do."

UKRAINE CLAIMS IT SHOT DOWN RUSSIAN HYPERSONIC MISSILE WITH US PATRIOT SYSTEM

The outside of the White House

The White House message on U.S. aid has shifted over time to favor heavily arming Ukraine. (Yasin Ozturk/Anadolu Agency via Getty Images)

The White House message on U.S. aid has shifted over time to favor heavily arming Ukraine. Biden hesitated, but later provided Ukraine with the Patriot missile system in December. Biden also agreed to provide tanks in January and joined a fighter jet coalition in May to train Ukrainians on F-16s.

CLICK HERE TO GET THE FOX NEWS APP 

The pro-Ukraine forces that reportedly used the U.S. equipment in Russia may not be officially a part of the Ukrainian military, Koffler said, but they are almost certainly linked.

"Ukraine wants to organize these sorts of raids in an unattributable fashion," she said, "In reality, it’s Ukraine, which is supported by the U.S."