KRAMATORSK, Ukraine — Ukrainian soldiers, seeking to spread Russian forces thin, launched a counteroffensive on Sunday in Kherson, the key southern city that Moscow considered so securely under its thumb that it had introduced the ruble.
Ukraine’s push in Kherson came as its forces were desperately battling to hold off Russia’s efforts to conquer and cut off a strategic strip of Eastern Ukraine that is central to Moscow’s struggling war effort, and it had the effect of expanding the battlefield.
The opening of the new front underlined that when it comes to territory in Ukraine, little is for keeps as each side tries to exploit the enemy’s shifting strategic vulnerabilities. That volatility promises to only increase as Ukraine receives more sophisticated long-range artillery, and soon possibly American missiles.
On Sunday, President Volodymyr Zelensky of Ukraine, who has appealed for those weapons, sought to build morale by visiting the country’s northeast, near Kharkiv, which is still under shelling.
“I want to thank each of you for your service,” Mr. Zelensky told his forces, marking their success this month in pushing Russians back from the outskirts of Kharkiv, Ukraine’s second-largest city. “You risk your life for all of us and our state.”
The city, which saw months of shelling that killed many civilians and forced tens of thousands to flee, was struck again hours after Mr. Zelensky left, according to Reuters.
The announcement of the Ukrainian counteroffensive — “Hold on, Kherson, we’re coming!” the military said Sunday morning on Twitter — signaled what may prove to be a new chapter in a war that has political, economic and humanitarian significance far beyond Ukraine’s borders.
Kherson, a port city in Ukraine’s agricultural heartland, was the first major city to fall as Russian forces swept north out of Crimea more than three months ago. After seizing it, Moscow used the city as a staging ground for operations across southern Ukraine.
But in recent weeks, Russian forces — stretched thin and taking heavy losses as they gain ground in the eastern Donbas region — have concentrated their efforts in the south on fortifying defensive positions. Satellite images have shown Russians scrambling to build fortifications in Kherson, where the shoots of an insurgency surfaced this month.
It was not clear if they were prepared for the Ukrainian counterattack.
The Ukrainian military headquarters said in a statement that its forces had broken through a Russian line of defense and pushed the Russians into less favorable terrain near the villages of Andriyivka, Lozove and Belihorka. The counteroffensive also sought to threaten Russia’s supply routes on bridges over the Dnipro River.
Ukraine had been telegraphing the counteroffensive for days, though it had said such a maneuver would require the Western artillery systems promised by the United States and other allies. It was unclear on Sunday what artillery Ukraine was using in its counteroffensive.
In a war that is increasingly becoming an arms race, powerful American-made howitzers reached Ukrainian forces this month, and Ukrainian troops recently received Harpoon anti-ship cruise missiles from Denmark. Ukraine’s defense minister, Oleksiy Reznikov, said they would be used to try to break Russia’s Black Sea blockade and to protect the port city of Odesa.
The Biden administration has also approved sending long-range multiple-launch rocket systems to Ukraine, a significant transfer that could hugely aid its defense.
With whatever hardware it has on hand, Ukraine seemed Sunday to be sending a message to Russia that it will not simply play defense in a battlefield of Russia’s choosing. Instead, Ukraine appears to be redrawing the map to include those places where diminished and hard-hit Russian forces have themselves dug into defensive positions.
Russia, after failing spectacularly to capture Kyiv, the capital, and Kharkiv has narrowed its focus on the 75-mile eastern frontline in the slender eastern Donbas region. It has devoted the bulk of its forces to pounding eastern Ukraine and capturing Sievierodonetsk, the last Ukrainian-controlled city in the Luhansk region, which is now at the heart of the conflict.
President Zelensky described the conditions in Sievierodonetsk over the weekend as “indescribably difficult.” Ukrainians call the route into the city from the west the “road of life,” as it is the only means to resupply their soldiers there. Russia has sought to cut that road off, and social media posts of burned Russian armored vehicles on the highway indicated they had at least briefly done so before being rebuffed.
Ukrainian military officials posted late Sunday on Facebook that Russia was “trying to gain a foothold on the northeastern outskirts of the city of Sievierodonetsk, conducting assault operations in the direction of the city center.”
Russia has been using long-range artillery to pound targeted towns into submission from a distance before surrounding and nibbling away at territory.
Russia has thermobaric warheads, a fearsome conventional weapon nicknamed the Heatwave, which send shock waves into bunkers and trenches. It has also claimed to have successfully test-fired a hypersonic Zircon cruise missile from the Barents Sea at a target more than 620 miles away. Hypersonic weapons, generally defined as those capable of flying at speeds over Mach 5 — five times the speed of sound — are at the center of an arms race among the United States, Russia and China.
As tactics, targets and weaponry in the conflict change, one constant is the human toll. The Ukrainian military said Sunday that Moscow had ordered hospitals in Crimea to stop treating civilians in order to care for wounded soldiers instead. The claim could not be independently verified.
Amid the loss of life and the destruction of civil society, European leaders are again calling for a cease-fire.
President Vladimir V. Putin of Russia said in a statement from the Kremlin that he was “open to renewing dialogue with Kyiv.”
The statement described a call he had on Saturday with the leaders of France and Germany. According to the Kremlin, Mr. Putin said that Western weapons deliveries could lead to “a further destabilization of the situation,” and he renewed his demand that the West drop sanctions against Russia to ease the export of food and fertilizer.
President Emmanuel Macron of France and Chancellor Olaf Scholz of Germany said that any resolution of the war must be negotiated between Moscow and Kyiv “with respect for the sovereignty and territorial integrity of Ukraine,” according to a statement from the office of the French presidency.
But Mykhaylo Podolyak, an aide to Ukraine’s president and envoy to peace talks held earlier in the three-month-long conflict, said in a post on Telegram over the weekend that Russia simply could not be trusted.
“Any agreement with Russia isn’t worth a broken penny,” Mr. Podolyak wrote. Until Russian troops withdraw from Ukraine, he said, “negotiations are being conducted by a separate ‘delegation’ on the front line.”