‘Lots of heavy fighting ahead’: U.S. officials urge caution after Ukrainian gains

The U.S. assesses that Ukraine’s battlefield gains on the eastern and southern fronts over the past three days are strategically important, but Kyiv is still far from a decisive victory, according to two U.S. officials.

In the east, Kyiv’s forces over the weekend captured the city of Lyman, a strategic railway hub, and continued to push east into the Donetsk region. Meanwhile in the south, Ukrainian soldiers broke through Moscow’s defensive lines in the Kherson region, gateway to the port city of Odesa.

These gains are a significant blow to Vladimir Putin, coming just days after he declared that Russia is annexing those regions — Donetsk and Kherson — as well as Zaporizhzhia and Luhansk after a series of sham referendums last week. On the home front, Putin is also facing challenges in mobilizing new troops for the fight, with reservists showing up with little training or equipment.

Ukraine’s victory in Lyman undermines Putin’s foothold in the eastern Donetsk region and “could turn into a cascading series of defeats for the Russians,” retired Army Lt. Gen. H.R. McMaster, former national security adviser, said Sunday on CBS’s “Face the Nation.”

“What we might be here is really at the precipice of really the collapse of the Russian army in Ukraine,” McMaster said. “They must really be at a breaking point.”

The advances in Kherson on Monday, meanwhile, represent a breakthrough after the incremental advances experienced by Ukrainian forces since they began their southern counteroffensive in September. Ukrainian troops burst through Russia’s defensive lines and advanced rapidly along the western bank of Dnipro River on Monday, recapturing a number of villages and threatening resupply lines for thousands of Russian troops.

“It shows the Ukrainians are capable of multiple operations,” said Mick Mulroy, a former deputy assistant secretary of defense and retired CIA official. “It also will be key to follow-on operations to include potentially taking control of water supply for the Crimean peninsula.”

But current officials cautioned that Kyiv’s most recent gains should not be overstated, and that Russian forces are holding steady in other areas such as nearby Bakhmut, in the Donetsk. The fight in the Donbas will be particularly grueling, as Russian forces are fighting from existing trenches and shelters they’ve held for years.

“There’s lots of heavy fighting ahead,” said one Defense Department official, speaking on condition of anonymity to discuss internal assessments.

“It’s important strategically, but they still have a long way to go,” said a second U.S. official, who also requested anonymity.

Looming over the battlefield gains is the simmering threat that the conflict could turn nuclear. Western officials are concerned Putin could use the annexations as an excuse to claim Ukrainian forces are attacking Russian territory and escalate the conflict, including potentially using a tactical nuclear weapon.

The U.S., however, has not received any indications that would prompt it to change its strategic posture, National Security Council spokesperson John Kirby, said on CNN Monday, adding “we’re watching this as closely as we can.”