Ukraine ‘pushed back’ Russian troops, Ukraine said on Saturday it had retaken a swath of the city from the Sievierodonetsk battlefield, in a rare counteroffensive against Russia’s main assault force that had been advancing steadily in the east.

The Ukrainian claim could not be independently verified and Moscow said its own forces were making progress there. But it was the first time Kyiv had claimed to have launched a major counterattack in Sieverodonetsk after days of giving ground there.

Russia has concentrated its forces on Sievierodonetsk in recent weeks for one of the war’s biggest ground battles, and Moscow appears to be betting its campaign on capturing one of the two eastern provinces it claims on behalf of separatist proxies.

Both sides have claimed to have inflicted huge casualties in the fight for the small industrial town, a battle that military experts say could determine which side has the momentum for a protracted war of attrition in the coming months.

Ukrainian Foreign Minister Dmytro Kuleba tweeted in response: “Calls to avoid humiliation of Russia can only humiliate France and any other country that requests it.

Serhiy Gaidai, the Ukrainian governor of Luhansk province, which includes Sievierodonetsk, said overnight that Ukrainian forces previously controlling only 30% of the city had mounted a counterattack and recaptured another 20% of the city.