Northeast Poland — While the U.S. Congress wrestles over the $60 billion aid package for Ukraine, the U.S. Army in Europe tells CBS News that if the money isn't approved by American lawmakers soon, it could go broke.

"We are running out of money," Col. Martin O'Donnell, spokesperson for the U.S. Army's combined Europe and Africa command, told CBS News in Poland, where American forces have been taking part in massive exercises. "We've got enough funds right now, but if nothing changes, we expect to run out of money before summertime."

O'Donnell's blunt assessment was the first time a senior Army official has gone on camera to warn about the urgency of the Ukraine funding package, which is crucial not only to Ukraine's war effort, but to the U.S. Army's wider operations across two vast regions.

The Army has been picking up the tab for hundreds of millions of dollars contributed by the U.S. to Ukraine's war effort, including for drills like the one taking place now in Poland. But if the aid package isn't approved, O'Donnell said the U.S. Army in Europe in Africa would run out of money by May or June.

The U.S. Army oversees the training of Ukrainian forces and the transportation of equipment through Europe into Ukraine, in addition to training and equipping U.S. troops across the region. All of that could grind to a halt, he said, if the additional funding for Ukraine isn't approved.

"There's a lot of risk right now if we don't get money," O'Donnell said. 

Asked what would happen if the money did run out, he said: "Don't really want to think about it. Both in terms of what we do on the two continents [Europe and Africa], and both in terms of support to Ukraine. It's at risk."

The Europe and Africa command has "made adjustments within our own organization, but we haven't compromised our readiness yet, and we haven't compromised the support we've provided to Ukraine. We haven't gotten to that point yet," said O'Donnell. "But, like I said, that point is rapidly approaching, where potentially difficult decisions will have to be made."

He stressed that he was only speaking about the budget and impact on the U.S. Army's operations in Europe and Africa, and noted that, "sure, there's still an army behind us, and there's still a Department of Defense also behind us. So, certainly money can be reallocated, but again, there's only so much money out there."

The Army's warning about the money crunch comes amid heightened concern over Russia's intentions for military expansion, with the Vladimir Putin's full-scale invasion of Ukraine about to enter its third year.

"I can't stress enough how important this assistance is for Ukraine. They need the assistance now," U.S. Ambassador to NATO Julianne Smith told CBS News on Thursday. "It's critical because, as we have seen many times in our history, if you don't stop a dictator they will ultimately keep going. The Ukrainians are fighting to defend their own territory. They are also fighting to defend the values that we hold dear. We need to stop Russia now in Ukraine, get the Russians out of Ukraine, so they don't get any second thoughts about going further westward and moving into NATO territory."

CBS News got exclusive access to the live-fire exercises taking place this week in northern Poland, right along one of the most sensitive borders separating democratic Europe from Russian territory.

Soldiers from the Army's 3rd Infantry Division, out of Fort Stewart, Georgia, were gaming out a scenario in which an unnamed adversary launched an attack on NATO's eastern flank. The operation for the soldiers was to recapture the ground and force that unnamed enemy to retreat.

CBS News watched as U.S. Bradley Fighting Vehicles charged through muddy fields, infantry troops spilled out and huge explosions rattled the ground as mine clearing weapons were put through their paces.

None of the soldiers or commanders taking part in the drill named the hypothetical "regional enemy" they were facing in the exercise, but the chosen location spoke volumes.

The exercise took place in the vicinity of the Suwalki Gap, a hilly area in northeast Poland that military planners consider NATO's Achilles heel.

To the west of the gap lies the Russian enclave of Kaliningrad. To the east, Russia's close ally Belarus, where Russia has deployed troops and, purportedly, nuclear weapons. Only around 40 miles of NATO territory — the Suwalki Gap — separates the Russian footholds.

If the Kremlin were to launch an incursion into Poland, and manage to take the gap, it would effectively cut off the Baltic States from the rest of their NATO allies.

The soldiers taking part in the U.S. Army drills this week are preparing for any eventuality, 3rd Infantry Battalion Commander Lt. Col. Timothy Decker told CBS News.

"We remain engaged in our training to develop our tactical proficiency and remain a lethal force in deterring aggression," he said.

But the Army says its ability to continue providing that lethal force and deterrent against America's adversaries is now under threat, and it's counting on the members of the U.S. Congress to get over their differences and keep the cash flowing, and fast.

In:
• War
• Ukraine
• Russia
• Vladimir Putin
• U.S. Army
• NATO

Charlie D'Agata

Charlie D'Agata his a CBS News foreign correspondent based in the London bureau.