Ukrainian President Volodymyr Zelenskiy says the country's armed forces have disrupted Russian plans for an offensive, with Moscow failing to reinforce its troops.
However, Chief of Russia's General Staff Valery Gerasimov, pointed to gains around major Ukrainian cities in the more than four-year-old conflict.
"The offensive is being conducted in all directions," the Russian Defence Ministry quoted Gerasimov as saying on its Telegram channel.
"In two weeks in March, 12 settlements have been liberated by units and military formations of the United Group of troops."
Gerasimov said Russian forces were "actively moving towards Sloviansk", a heavily defended town in eastern Ukraine's Donetsk region long seen as one of Moscow's major targets.
He said Kostiantynivka, another town long subject to Russian pressure, was now 60 per cent in Russian hands, with Ukrainian forces "taking all possible measures to stop our advance".
"In Kostiantynivka itself, there are street battles in the northwestern district," Gerasimov was quoted as saying, adding that assault troops were pushing their way into the city.
Russian forces were also making headway further south in Zaporizhzhia region, were "actively advancing westward" and were also continuing to set up buffer zones in Kharkiv and Sumy regions on the border.
Zelenskiy, speaking in his nightly video address after meeting Ukraine's top commander, Oleksandr Syrskyi, said Russian assaults had become less intense.
"Ukraine's defence forces have disrupted Russia's strategic offensive operation that the enemy had planned for March," he said.
"Although attacks are constant and assaults continue, their intensity and the scale of the confrontation are not what Russia had planned and what its command promised to Russia's political leadership."
Zelenskiy and Syrskyi have pointed in recent weeks to successes in Zaporizhzhia region, recapturing about 400sq/km of territory and retaking eight settlements.
Russia's top military offices have repeatedly said their forces have been making constant gains all along the front line.
The Ukrainian DeepState military blog, which relies on open sources to determine the position of both sides, said Russian forces were attempting a breakthrough in Kostiantynivka and had made some gains around Sloviansk.
The issue of territory remains the key sticking point in slow-moving negotiations aimed at clinching a settlement to the conflict. Russia is pressing for Ukraine to give up all of the Donbas (made up of the Donetsk and Luhansk regions), including areas its forces have not captured, a demand Zelenskiy has rejected.
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