Russia is “suffering huge losses” and losing hard-fought ground in the Ukrainian city of Severodonetsk after invading units started retreating from the key industrial center, Ukrainian officials asserted Saturday.

The dramatic turnabout, which could not be independently confirmed, represented a rare successful counter-offensive against Russian forces, which had recently been steadily advancing in Ukraine’s eastern territories.

It was the first time Ukraine claimed to have conducted a large counter-attack in Severodonetsk, a city of 100,000 and the last major municipality in the disputed Luhansk oblast under Ukrainian control, after days of losing ground in the country’s embattled east.

Russia had “previously managed to capture most of the city,” Sergiy Haidai, the governor of the Luhansk region said in a televised address Saturday, The Guardian reported. “But now our military has pushed them back.”

Later Saturday, Oleksandr Stryuk, the head of the city’s military operations, said that Ukrainian forces were able to build a line of defense in Severodonetsk, according to The Kyiv Independent.

Both sides of the war have claimed to have inflicted huge casualties in the fighting for the city — a battlefront that military experts believe could determine which of the two countries has the momentum for a prolonged war of attrition in coming months.

Haidai — who oversees the territory where Severodonetsk is located — said he expects the new supply of US-made weapons to seal the deal in gaining back control of the city....