KHARKIV, Ukraine — The Ukrainian Army was close to losing a key battle of the war. A single, tenuous supply road for Ukrainian soldiers fighting in the streets of the eastern city of Bakhmut was taking fire. A general called the threatened road the “last breathing tube.”
This dire assessment of fighting in Bakhmut, one of the longest running and most lethal battles of Russia’s war in Ukraine, appears in a new batch of classified documents that appears to detail American national security secrets.
The assessment captures only one moment, from late February, in the now 10-month-long fight for Bakhmut, a midsize university and mining town of questionable strategic significance but one that both sides have freighted with political meaning.
The city is now mostly in ruins, as fires sweep through buildings and soldiers fight in fierce, block-by-block combat.
Ukrainian soldiers have fought human-wave assaults by former convicts in the Wagner mercenary group and by elite Russian special forces troops, and they have endured round-the-clock artillery bombardments.
However, the leaked assessment focused on a related theater of the battle for Bakhmut, including two flanking maneuvers by the Russian Army through fields and villages to the city’s northwest and southwest that were intended to encircle Ukrainian troops by cutting off supply roads.
It described internal Ukrainian military deliberations on how to respond, with commanding generals deciding to deploy elite units from the military intelligence agency to push back the Russians.
The documents, from late February and early March but found on social media sites in recent days, outline critical shortages that the Ukrainian military is facing. The intelligence reports show that the United States also appears to be spying on Ukraine’s top military and political leaders, a reflection of Washington’s struggle to get a clear view of Ukraine’s fighting strategies.
The leak pulled back the curtain on decision-making inside the Ukrainian military command in a way not seen in public before.
The Ukrainian military has effectively safeguarded key secrets throughout the war, including foreshadowing of the successful, surprise counterattack last summer in the Kharkiv region that swept over Russian lines. Ukrainian officials have called the document leak a Russian propaganda ploy.
“Ukrainian forces as of 25 February were almost operationally encircled by Russian forces in Bakhmut,” the leaked intelligence assessment noted.
Senior U.S. officials said an inquiry, launched by the Federal Bureau of Investigation, would try to move swiftly to determine the source of the leak. The officials acknowledged that the documents appear to be legitimate intelligence and operational briefs compiled by the Pentagon’s Joint Staff, using reports from the government’s intelligence community, but that at least one had been modified from the original at some later point.
It said that Gen. Kyrylo Budanov, Ukraine’s director of military intelligence, offered to deploy elite units under his command for two weeks to push back Russian troops threatening the supply road. It cited General Budanov as describing Ukraine’s position at the time as “catastrophic.”
Roman Mashovets, an adviser to Andriy Yermak, President Volodymyr Zelensky’s chief of staff, also offered a cleareyed assessment in a briefing, the document says.
Mr. Mashovets advised that a single supply road, winding over hills to the west of Bakhmut, remained accessible for the forces inside the city — and that it was under artillery fire.
“Mashovets reported that, for those reasons, the morale in Bakhmut was low, with the Ukrainian forces under the impression that they were almost operationally encircled,” the leaked assessment said.
In the fighting on the plains of southeastern Ukraine, encirclement poses a grave danger feared by soldiers on both sides.
Once surrounded, ammunition quickly runs low, wounded soldiers cannot be evacuated and those still fighting are at risk of being overrun and killed. The commander of ground forces in the east, Gen. Oleksandr Syrsky, called the single supply road the “last breathing tube” and asked that Kraken, a unit in the military intelligence agency, be deployed to Bakhmut, the document said.
The leak opened a window on internal deliberations in the Ukrainian leadership and showed a Western intelligence assessment that Bakhmut was teetering by late February.
Yet the broader picture it paints was hardly secret. Russian forces had closed in on supply roads in February, according to the military’s daily briefings and public comments by soldiers fighting in the area, before Ukraine sent in reinforcements. A variety of elite units joined the fight.
This fighting, which came after the intelligence assessment was written, was successful in pushing Russian forces far enough from the roads to allow resupply of soldiers in the city and evacuation of the wounded.
But it came at a strategic cost for Ukraine, which has been seeking to retain its best trained and equipped soldiers for a counteroffensive anticipated in the coming weeks or months.