KYIV, Ukraine >> Ukrainian forces were making a major effort to end a battlefield stalemate and punch through Russian defensive lines in southeast Ukraine for a second day today, in what may herald the start of a long-anticipated counteroffensive after 15 months of war.

Russian officials seemed to be trying to portray the Ukrainian attacks as the start of the counteroffensive, saying that Moscow’s forces foiled at least one assault. While not explicitly confirming such a large-scale effort, Kyiv authorities said their forces were indeed increasing offensive operations and making gains, but suggested some of the Russian announcements were misinformation.

Vladimir Rogov, an official in the Russia-backed administration of Ukraine’s partly occupied Zaporizhzhia province, said fighting resumed on its border with the eastern Donetsk province today after Russian defenses beat back a Ukrainian advance the previous day.

“The enemy threw an even bigger force into the attack than yesterday (Sunday),” and the new attempt to break through the front line was “more large-scale and organized,” Rogov said, adding: “A battle is underway.”

Rogov interpreted the Ukrainian military movements as part of an effort to reach the Sea of Azov coast and sever the land corridor to the Crimean Peninsula, which Moscow annexed in 2014. Analysts have long viewed that strategy as likely because it would cut the Russian forces in two and severely strain supplies to Crimea, which has served as a key Russian military hub in the war that started Feb. 24, 2022.

Rogov’s comments came after Moscow also said its forces thwarted large Ukrainian attacks in Donetsk province, near its border with the Zaporizhzhia province.

Reacting to Russia’s declarations that it repelled Ukrainian offensives, a U.S. official said on the condition of anonymity to discuss sensitive matters: “We have no reason to believe any Russian action has had any spoiling effect on pending or ongoing Ukraine operations.”

Ukrainian Deputy Defense Minister Hanna Malyar said the Ukrainian military has scored gains.

“Despite fierce resistance and attempts of the enemy to hold the occupied lines and positions, our units moved forward in several directions during the fighting,” she said.

Malyar drew no distinctions between phases of the war, insisting that Ukraine’s defense against Russia’s invasion “contains everything, including counter-offensive actions.” She acknowledged that Kyiv’s forces “in some areas … are shifting to offensive operations.”

Sir Richard Barrons, a general who is a former commander of the U.K. Joint Forces Command, said that Ukraine was “clearly in the preliminary phase” of its counteroffensive and would probe Russian defenses to find weak spots, then focus its resources to ram through them and hold ground. Barrons, now co-chair of the U.K.-based strategic consulting firm Universal Defence & Security Solutions, told The Associated Press the Ukrainians are “trying to increase the chances of surprise about when you do it, where you do it and how you do it.”

Commenting on the Russian military’s assertion that it thwarted a big Ukrainian attack, he said it could be part of Ukrainian efforts to probe Russian defenses and test its units in combat. He added that Moscow could have exaggerated the scale of the fighting and claimed victory to assuage its domestic Russian audience.

Barrons predicted that the Ukrainian counteroffensive would involve a series of moves and take weeks.

“It’s a process, not an event,” he said.

Ukraine often waits until the completion of its military operations to confirm its actions.

A Ukrainian Defense Ministry video showed soldiers putting a finger to their lips in a sign to keep quiet. “Plans love silence,” it said on the screen. “There will be no announcement of the start.”

Zaporizhzhia and Donetsk are two of the four provinces that President Vladimir Putin claimed as Russian territory last fall and which Moscow partially controls.

Russia’s Defense Ministry said it had pushed back a “large-scale” assault Sunday at five places in Donetsk province. The announcement couldn’t be independently verified, and while Ukrainian officials reported fighting in that area, they didn’t confirm a retreat.

Russian Defense Ministry spokesman Igor Konashenkov said in an unusual overnight video that 250 Ukrainian personnel were killed in the fighting in Donetsk province, and 16 Ukrainian tanks, three infantry fighting vehicles and 21 armored combat vehicles were destroyed.

In response, the Center for Strategic Communications of the Armed Forces of Ukraine said Russian forces were “stepping up their information and psychological operations.”

“To demoralize Ukrainians and mislead the community (including their own population), Russian propagandists will spread false information about the counteroffensive, its directions and the losses of the Ukrainian army. Even if there is no counteroffensive,” a statement on Telegram read.

Ukrainian President Volodymyr Zelenskyy said that the Russians overreacted to its latest push.

“We see how hysterically Russia perceives every step we take there, every position we take,” Zelenskyy said in his nightly address.

Ukrainian officials have said for months that a spring campaign with advanced weapons supplied by Western allies to reclaim territory seized by Russia during the war was planned, but they have kept quiet about when, how and where it might start, or whether it had already been launched.

Recent military activity, including drone attacks on Moscow, cross-border raids into Russia and sabotage and drone attacks on infrastructure behind Russian lines, has unnerved Russians. Analysts say those actions may represent the start of the counteroffensive.

In other disruption, TV and radio broadcasts in several regions of Russia were hacked today, according to Kremlin spokesman Dmitry Peskov. A fake broadcast featured a voice impersonating Putin and stated that Ukrainian forces had invaded the Belgorod, Bryansk and Kursk regions of Russia.

Those Russian regions have occasionally been targeted in cross-border strikes during the war.

The impersonator announced that martial law was declared in those regions, where people were urged to evacuate, and all Russians eligible for military duty were being mobilized.

The Russian military said today it repelled the latest Ukrainian incursion into the Belgorod region, on the border in Ukraine. Russians who purport to be fighting alongside Ukrainian forces said they attacked on Sunday. They were driven back by airstrikes and artillery fire, according to the Russian Defense Ministry.

At least two factors have been at play in the counteroffensive’s timing: better ground conditions for the movement of troops and equipment after the winter, and the deployment of more advanced Western weapons and training of Ukrainian troops to use them.

Ukraine’s Western allies have sent the country more than 65 billion euros ($70 billion) in military aid to help its defense. Driving out the Kremlin’s forces is a daunting challenge for Kyiv’s planners. Russia has built extensive defensive lines, including trenches, minefields and anti-tank obstacles.

After months of a battlefield stalemate, with neither side making significant gains and suffering losses of personnel and weapons, Ukraine could launch simultaneous pushes in different areas of the front line that stretches for around 1,100 kilometers (nearly 700 miles), analysts say.

In the devastated eastern city of Bakhmut, the site of the war’s longest and bloodiest battle, Malyar, the deputy defense minister, said Ukrainian forces are advancing and “occupy dominating heights.” Zelenskyy said in his nightly address, “Bakhmut direction — well done, warriors!”

The leader of Russia’s Wagner mercenary group, Yevgeny Prigozhin — a frequent critic of his country’s military brass whose statements are sometimes unreliable — said that Russian forces lost control of part of the village of Berkhovka outside Bakhmut. Prizoghin said last month that his forces had seized all of the city of Bakhmut, with Ukrainian forces remaining in control of many surrounding areas.

Danica Kirka contributed to this story from London.