Ukraine has stepped up its bid to retake the Russian-controlled south of the country by trying to bombard and isolate Russian troops in hard-to-resupply areas, but said it saw signs Moscow was redeploying its forces to defend the territory. Ukraine’s southern Kherson region, which borders Russian-annexed Crimea, fell to Russian forces shortly after the start of what Moscow calls “a special military operation” on February 24. Ukraine, which describes Russia’s actions as an imperial-style war of conquest, said on Thursday that its planes hit five Russian strongholds around the city of Kherson and another town in the region. British military intelligence, which assists Ukraine, said it was possible Ukrainian forces had also set up a bridgehead south of a river that runs along the wider northern Kherson region. “Ukraine’s counteroffensive in Kherson is intensifying,” it said in a statement. Ukraine says it has recaptured some small settlements on the northern edge of the region in recent weeks as it tries to push back Russian forces, a possible prelude to what Kyiv has described as a major counteroffensive to retake the south. Russia said on Thursday it was not alarmed, with the defense ministry saying its warplanes attacked a Ukrainian infantry brigade in the northern Kherson region and killed more than 130 of its soldiers in the past 24 hours. Kirill Stremousov, the deputy head of the Russian-appointed military-civilian command that commands the Kherson region, also rejected Western and Ukrainian assessments of the situation on the battlefield. “(Ukrainian President Volodymyr) Zelensky’s statement that the Kherson region will be liberated in three to six weeks is… a lie. All these counterattacks leading to a large number of Ukrainian casualties are not succeeding,” Stremusov told Russia’s RIA news agency on Wednesday. Ukraine has used long-range missile systems supplied by the West to severely damage three bridges on the Dnipro River in recent weeks, making it harder for Russia to supply its forces on the west bank. British intelligence said the strategy had begun to isolate Russian forces in the Kherson region. “Russia’s 49th Army, located on the west bank of the Dnipro River, now looks very vulnerable,” it said in a briefing. The city of Kherson was now virtually cut off from the other lands held by Russia. “His loss would seriously undermine Russia’s efforts to label the occupation a success,” it said. A Ukrainian strike on Wednesday on the Antonivskyi Bridge, the only span serving the city of Kherson, brought traffic to a standstill. This forced Russia to open a ferry service, the route of which it said would be constantly changed for security reasons. Oleksiy Danilov, secretary of Ukraine’s National Security and Defense Council, tweeted that Russia was massing “the maximum number of troops” in the direction of the Kherson region, but gave no details. Oleksiy Arestovych, an adviser to President Zelensky, said Russia was conducting a “massive redeployment” of forces from the east to the south, amounting to a strategic shift from offense to defense. RIA reported on Thursday that Russian security services discovered a group of Ukrainian agents in Kherson who had been paid to map the coordinates of Russian forces there in Ukraine for artillery targeting. Zelensky said Ukraine would one day rebuild the Antonivskyi Bridge over the Dnipro and other crossings in the region. “We are doing everything to ensure that the occupying forces do not have logistical opportunities in our country,” he said in a speech on Wednesday evening, on the eve of Ukraine’s annual State Day. Oleksiy Gromov, a senior official of the Ukrainian military’s general staff, told a news conference on Thursday that the bridge is of great importance to Russia’s defense effort and Ukraine’s attempted offensive. “We have repeatedly hit the Antonivskyi bridge … There is significant damage to the bridge structures,” Gromov said. Russia continues to carry out its own daily strikes against targets across Ukraine. Five people were killed and 25 wounded in a Russian missile attack on a flight school in the central Ukrainian city of Kropyvnytskyi on Thursday, the regional governor said. Fierce fighting is also underway in eastern Ukraine, where Russia is trying to take control of the entire industrialized Donbas region. Ukraine confirmed late Wednesday that Russian forces had seized the Soviet-era coal-fired power plant in Vuhlehirsk, Ukraine’s second largest, in what was Moscow’s first major gain in the Donbass in more than three weeks. Kyiv played down the significance of the setback. On the front line near Izium, Kharkiv region, Ukraine’s Carpathian Sich battalion has been joined by foreign fighters. They face daily artillery bombardment, but say Ukraine’s fight against Russian forces is worth the risk. Reuters Our Morning Update and Afternoon Update newsletters are written by Globe editors, giving you a concise summary of the day’s most important headlines. Sign up today.