Russia says it repelled a large-scale Ukrainian assault.

Ukrainian ground forces tried to break through Russian defenses in eastern Ukraine, in an area of the front that had not shifted significantly for months, and staged large-scale assaults across much of the frontline, Russian authorities and military bloggers aligned with the Kremlin said Monday.

Ukraine has remained silent about military operations after months of preparing for a major counteroffensive in the war. Consequently, Russian reports were expected to signal the start of military action before any formal Ukrainian announcements. The only indication from the Ukrainian side that an operation may have started was a video released by the military Sunday showing soldiers putting a finger to their lips, asking for silence.

Two unverified Russian reports said Ukrainian forces had pushed through Russian defenses in two areas. While the Russian Ministry of Defense said early Monday that a major Ukrainian operation had begun along multiple sections of the front in the Donetsk region, it said the Ukrainian attack had been repelled. Moscow’s reports of the offensive and Ukrainian casualties could not be corroborated. Tass, the Russian news agency, cited the ministry spokesman, Igor Konashenkov.

There was no immediate response from the Ukrainian authorities to the Russian claim.

By early Monday, a Russian Telegram channel that reports on the war said Ukrainian forces had breached a first line of Russian defenses near the town of Velyka Novosilka in Donetsk, and reclaimed two villages as Russian forces fell back to reserve positions.

Buttressing the Russian reports the counteroffensive had begun, independent American military analysts said they believed Ukrainian units had begun an initial thrust to determine the position and strength of Russia’s forces.

The various reports of combat maneuvers across the front were hard to decipher and it was unclear what operations were part of a main attack and which could be feints or diversions. But a thrust to test Russian lines would be a traditional tactic of the kind Americans have been training the Ukrainians to undertake.

The Russian reports of the fighting Sunday night and Monday morning were of movements of larger units, a potential signal that Ukraine had pushed its NATO-trained forces into the fight.

Rybar, another Russian Telegram channel, said Ukrainian forces had launched an attack in the Zaporizhzhia region, to the west of Donetsk, with company sized units, or groups of about 100 soldiers, supported by tanks, and had advanced about 200 yards. It said Russian forces had destroyed two Ukrainian tanks with anti-tank missiles. The claims could not be independently verified.