KYIV, Ukraine — The Ukrainian military announced on Monday that it had launched offensive operations in multiple areas along the front line in the Kherson region in southern Ukraine, perhaps signaling the start of a broad and long anticipated counteroffensive aimed at retaking territory seized by Russia.
Fighting along a swath of the front line escalated sharply on Monday, according to Ukrainian military and civilian officials, and the Ukrainian government said that its military had “breached the occupiers’ first line of defense near Kherson.”
The Ukrainian military also claimed on Monday to have struck a large Russian military base behind Russian lines in the Kherson region, destroying it. It was not immediately possible to verify the claims.
Across the Kherson region — whose capital was the first major city to fall to Russian forces after President Vladimir V. Putin invaded Ukraine in February — electrical networks blinked out amid the fighting on Monday, and Russian media reported evacuations from towns in the area.
A United States defense official lent support to the idea that Ukraine was escalating its offensive in the south, saying: “The announced offensive shows the Ukrainians’ appetite for progress on the battlefield.” The official, speaking on condition of anonymity to discuss sensitive military matters, added that the Pentagon remained cautious about whether Ukraine’s current military capabilities were sufficient to make significant gains.
It remained unclear if this was the start of the southern counteroffensive that Ukraine has telegraphed for months, or a continuation of strikes in the south that Ukraine has been carrying out for the last several weeks.
Ukrainian officials were circumspect in their statements on Monday.
“Anyone want to know what our plans are?” President Volodymyr Zelensky said in his nightly address. “You won’t hear specifics from any truly responsible person. Because this is war. And this is what it is during the war.”
The spokeswoman for the southern military command, Nataliya Gumenyuk, said that Ukraine had begun “offensive actions on many directions” in the south. She later issued a statement saying: “Every military operation requires silence,” and “everyone needs to be patient.”
A Russia-installed official in Kherson initially denied an offensive was even taking place, but Russia’s Ministry of Defense later acknowledged that Ukrainian troops had launched attacks in three directions — although it said those efforts had “failed miserably.” The ministry said Ukrainian forces had suffered “heavy losses” in the attempt, but provided no evidence to support those claims.
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Junior Sgt. Dmytro Pysanka, a Ukrainian soldier stationed on the Kherson front, said “our offensive is ongoing.”
“I don’t know what’s going to happen next and how, but so far all goes according to the plan,” he said in a text message.
The reports of intensifying fighting came as the director general of the International Atomic Energy Agency announced that a team of nuclear experts would visit the Zaporizhzhia Nuclear Power Plant, which lies to the north of Kherson. An official familiar with the agency’s plans who spoke on the condition of anonymity said the I.A.E.A. team would arrive there on Wednesday at the earliest.
Mr. Zelensky’s government has been under pressure to begin a counteroffensive intended to push Russian troops from Kherson and the western bank of the Dnipro River before the rainy season leaves fields muddy and impassable or European support wavers amid rising energy prices. Ukraine has signaled the start of offensive operations multiple times since May, though with little land changing hands.
Mr. Zelensky vowed on Monday evening that Russian soldiers would be pushed back to the country’s borders, reclaiming separatist territory and Crimea, which Russia illegally annexed in 2014. Invading forces should flee, or surrender, he said.
“If they do not listen to me, they will deal with our defenders, who will not stop until they liberate everything that belongs to Ukraine,” he said.
Natalia Yermak and Ivan Nechepurenko contributed reporting.
