Fighting is raging at several points along the front lines, Russian and US officials say.

Ukrainian forces stepped up their artillery and ground assaults in a flurry of offensive military activity that swept along multiple sectors of the frontline on Monday, US and Russian officials said.

Ukraine has remained silent on military operations after months of preparations for a major counter-offensive in the war. But US officials, speaking on condition of anonymity, said the spate of attacks was a possible indication that Kiev’s long-planned counter-offensive against Russian forces had begun.

The officials based their assessment in part on information from US military satellites, which detected an increase in action from Ukrainian military positions. The satellites have infrared capabilities to track artillery fire and missile launches.

One problem in determining the exact start of a counter-offensive, beyond Ukraine’s operational security measures, is that the fighting may very well begin with feints or diversions that are difficult to decipher.

Russia’s defense ministry announced on Monday that a major Ukrainian operation had begun at five locations along the front in an eastern region, Donetsk, saying it had repelled the attacks and inflicted casualties on Ukrainian forces. Moscow’s reports could not be confirmed.

However, Russian bloggers affiliated with the Russian military reported that Ukrainian forces had advanced in some areas, including taking the village of Novodonetske in the Donetsk region.

Those allegations could not be immediately verified and there was no immediate response from the Ukrainian authorities to the statements.

The reported Ukrainian attacks took place east of where many analysts expected the counter-offensive to begin. But even by starting in that eastern area, Ukraine could achieve the same goal: move south toward the Sea of ​​Azov and cut the “land bridge” connecting Russian-occupied Crimea to Russia.

Supporting reports that the counter-offensive may have begun, US military analysts said they believed Ukrainian units had launched an initial strike to determine the position and strength of Russian forces. Such moves would be traditional tactics of the sort the Americans have been training Ukrainian troops for.

Much depends on Ukraine’s efforts to reclaim territory and free Ukrainians from life under occupation. Success could help Kiev push for longer-term commitments to additional military aid and security guarantees from the West. It could also strengthen President Volodymyr Zelensky’s hand in peace talks with Russia. Failure, or a lack of dramatic rapid progress, could complicate Ukraine’s ability to get further aid from the West and hamper Kiev’s push for additional security guarantees at the NATO summit. harder this summer.

Whatever exactly happened, the relative calm experienced by most of the long battle lines stretching across Ukraine was shattered.

The front in southern and eastern Ukraine has been largely static for months, with the exception of heavy fighting in Bakhmut and some test operations by small Ukrainian units. In northeastern Ukraine, pro-Ukrainian forces also began cross-border raids into Russia last month.

Initial reports of fighting on Sunday night and Monday morning were larger unit movements, a possible signal that Ukraine had pushed its NATO-trained troops into battle.

A Russian Telegram channel covering the war said early Monday morning that Ukrainian troops had breached a first line of Russian defenses near Velyka Novosilka in Donetsk — not far from Novodonetske — and recaptured two villages as Russian troops fell back to reserve positions. The fighting at another location was confirmed by the head of the regional occupation authority in the Zaporizhia region, Vladimir Rogov, in a message on Telegram. The bloggers’ posts about Novodonetske began to appear on Monday afternoon.

Ukrainian officials have not told their US counterparts exactly when the counter-offensive will begin, but have given them a time frame in which they intended to begin their push against Russian forces. Sunday fell within that time frame, US officials said, speaking on the condition of anonymity to discuss sensitive information.

The Pentagon has been training new Ukrainian units in hopes they have the power to turn the tide of the battle, but some US officials have noted that entrenched Russian defenders can be difficult to dislodge.

Since March, smaller Ukrainian units of tanks and armored personnel carriers have been conducting operations along the battle lines in Zaporizhzhia province. The real beginning of any offensive attack, if that’s what started on Sunday, would be larger units not just conducting probing attacks, but actively trying to break through the Russian defenses.