As Russian President Vladimir Putin’s invasion of Ukraine has continued for almost four weeks with his military forces now stalled in Ukraine, the Pentagon stated on Tuesday that Russia’s combat power has dropped significantly.

“We’ve assessed, for the first time, that the Russians may be slightly below a 90% level of assessed available combat power,” a senior defense official told reporters, according to Fox News.

However, the official warned that “It is not an assessment of all Russian military power.”

“Security officials continue to warn that Putin may be looking to bring supplemental forces into Ukraine to aid his war as Russian ground forces remain stalled across the country,” Fox News reported. “But there is scant evidence that any foreign fighters have headed to Ukraine despite reports that Putin has offered incentives to fighters from nations like Syria.”

The senior defense official said that there are indications of ongoing “discussions” by Russia to aid its invasion “both in terms of resupply and also reinforcement,” but there is no indication that a plan has begun.

If Putin does send reinforcements, the senior defense official said they would likely come from troops stationed outside Russia first.

“Of the battalion tactical groups that Mr. Putin has available to him across Russia, he’s used about 75% in this particular operation,” the senior defense official explained.

“So I think our assumption would be he’d pull from outside the country first.”

As Russian forces have failed to make progress in their invasion for weeks, the official said it appears that Ukraine could be able to take back lost territory.

“We’re definitely seeing anecdotal evidence that the Ukrainians are not only defending well, where they choose to defend, but they are making efforts to take back territory,” the official said.

A senior defense official also said that many Russian troops are even “suffering from frostbite.”

“Because they lack the appropriate cold-weather gear for the environment that they’re in,” the official said. “In addition to food and fuel, even in terms of personal equipment for some of their troops, they’re having trouble.”