A jubilant Ukrainian President Volodymyr Zelensky taunted Moscow on a video camera, saying “the Russian army these days is showing its best, showing its back.” Ukraine’s swift action to retake Russian-held areas in the northeastern region of Kharkiv forced Moscow to withdraw its troops to prevent them from circling and leaving behind a significant number of weapons and ammunition in a hasty retreat. On Sunday, the president also released a video of Ukrainian soldiers raising the national flag over Chkalovsk, another town they captured from the Russians in the counterattack. Ukraine’s military chief, General Valerii Zaluzhny, said Ukraine has liberated about 1,160 square miles since early September and is within about 30 miles of the border with Russia. The retreat of Moscow’s forces marked the biggest battlefield success for Ukrainian forces since they thwarted a Russian attempt to seize the capital, Kyiv, at the start of the war in February. Ukraine’s offensive in the Kharkiv region came as a surprise to Moscow, which had moved many of its troops from the region to the south in anticipation of the main Ukrainian counteroffensive there. In an awkward attempt to save face, the Russian Defense Ministry said the withdrawal of troops from Izyum and other areas in the Kharkiv region was intended to bolster Russian forces in the neighboring Donetsk region to the south. The cluster of Russian forces around Izyum has been key to Moscow’s bid to seize the Donetsk region, and the retreat will dramatically weaken Russia’s ability to attack the Ukrainian strongholds of Sloviansk and Kramatorsk just to the south. Igor Strelkov, who led Russian-backed separatists in the first months of the Donbass conflict when it erupted in 2014, scoffed at the Russian Defense Ministry’s explanation for the retreat, suggesting that Russia’s surrender of territory near the border to Ukraine was “contribution to the Ukrainian settlement”. The retreat drew angry comments from Russian military bloggers and nationalist commentators, who decried it as a major defeat and urged the Kremlin to respond by stepping up the war effort. Many sharply criticized Russian authorities for going ahead with fireworks and other lavish celebrations in Moscow that marked a city holiday on Saturday despite the devastation in Ukraine. There were also reports of some local Russian councils calling on President Vladimir Putin to step down, in a possible sign of growing internal opposition to the all-powerful leader. Pro-Kremlin political analyst Sergei Markov criticized the celebrations in Moscow as a grave political mistake. “Fireworks in Moscow on a tragic day of Russia’s military defeat will have extremely serious political consequences,” Mr Markov wrote on his messaging app’s channel. “Authorities should not celebrate when people mourn.” In a sign of a possible rift in Russian leadership, Ramzan Kadyrov, the Kremlin-backed leader of Chechnya, said the retreat from the Kharkiv region stemmed from blunders by the Russian military leadership. “They have made mistakes and I think they will draw the necessary conclusions,” Mr Kadyrov said. “If they do not make changes in the strategy of conducting the special military operation in the next day or two, I will be forced to contact the leadership of the Ministry of Defense and the leadership of the country to explain the real situation on the ground. .” Despite Ukraine’s gains, US Secretary of State Antony Blinken and Jens Stoltenberg, NATO’s secretary general, warned that the war would likely drag on for months. In another major development on Sunday, the Zaporizhzhia nuclear power plant, Europe’s largest, was reconnected to Ukraine’s electricity grid, allowing engineers to shut down its last operating reactor in a bid to avoid a radioactive disaster as fighting rages in region. For the past several days, the plant had been operating in “island mode,” with only one of its six reactors working to power cooling systems and other critical equipment. (With agencies)