Russia has appointed Valery Gerasimov, chief of the general staff, as its overall commander for the war in Ukraine, in the latest of several major shake-ups of Moscow’s military leadership during the stumbling invasion of its neighbour. In a statement on Wednesday, the defence ministry said that Gerasimov’s appointment constituted a “raising of the status of the leadership” of the military force in Ukraine and was implemented to “improve the quality … and effectiveness of the management of Russian forces”. Sergei Surovikin, a notorious general nicknamed “General Armageddon” by the Russian media, who was appointed as overall commander of the army in October, would stay on as a deputy of Gerasimov, the defence ministry said. Gerasimov, like the defence minister, Sergei Shoigu, has faced sharp criticism from Russia’s hawkish military bloggers for multiple setbacks on the battlefield and Moscow’s failure to secure victory in a campaign the Kremlin had expected to take just a short time. The latest change in leadership comes amid ongoing tensions between senior figures in charge of Russia’s war in Ukraine. On Tuesday evening, the head of Russian’s Wagner mercenary group, Yevgeny Prigozhin, lashed out against the country’s defence ministry, boasting that his combat experience was “in many ways significantly superior to those who have been in the service of the ministry of defence for decades”. Prigozhin, who has previously criticised Gerasimov and Shoigu, made his statements as he claimed his Wagner army had taken control of the small salt-mining town of Soledar. However, the Ukrainian president, Volodymyr Zelenskiy, mocked the claims, saying in a video address that fighting was still going on. “The terrorist state and its propagandists are trying to pretend” to have achieved some successes in Soledar, Zelensky said in his daily address, “but the fighting continues”. He said the Donetsk front was holding “and we are doing everything to strengthen the Ukrainian defence without any break, even for one day.” The claims about the status of the fighting on the eastern Donbas came as Poland announced that it planned to transfer 10 German-made Leopard 2 main battle tanks to Ukraine, in a move with wide significance. Speaking on a visit to Lviv on Wednesday, the Polish president, Andrzej Duda, said: “A company of Leopard tanks will be handed over as part of coalition building. We want it to be an international coalition.” The transfer would require permission from Germany, which Kyiv has been pressing separately to supply Leopard 2s, perhaps suggesting a softening of Germany’s stance on the transfer of main battle tanks after recent contacts between Warsaw and Berlin. However, a German government spokesperson said it was not aware of any requests from allies to send the tanks to Ukraine. The Russian capture of Soledar and the town’s saltmines would have symbolic, military and commercial value for Moscow. But the situation in and around Soledar appeared fluid and neither claim could be independently verified. Prigozhin had released a photo showing him with a group of his fighters and a tank, which he said was taken in one of the tunnels of a saltmine in the south-west of Soledar. He also said that only units of his paramilitary company – many of them convicts who had been offered a pardon if they fought for him – had been involved in fighting for the city. Footage posted from Soledar by a Ukrainian soldier from a drone unit – identified by the call sign Maygar at 10am on Wednesday – suggested heavy clashes were continuing but Ukrainian forces were still holding positions. “This is the sound of Soledar,” he said to the background noise of constant artillery strikes. “Local fights are happening from time to time and artillery is working on both sides.” Accounts from Ukrainian soldiers on that sector of the front suggested Russia had moved Wagner fighters from Bakhmut to focus solely on the battle for Soledar. The Ukrainian deputy defence minister Hanna Maliar said: “Hard battles are going on to keep Soledar.” She added: “The enemy does not pay attention to the large losses of its personnel and continues to actively storm. The approaches to our positions are simply littered with the bodies of dead enemy fighters.” However, the Ukrainian military’s morning summary made only one mention of Soledar, listing it as one of several areas being shelled in the Donetsk region. A Ukrainian soldier who has been posting video updates from the Bakhmut area described the fighting in Soledar as fierce, with contested buildings changing hands multiple times and soldiers suffering frostbite. Russian forces have recently focused their efforts on the capture of Soledar as part of their ambition to take the nearby strategic city of Bakhmut and Ukraine’s larger eastern Donbas region, leading to fierce battles in sub-zero temperatures over the past five days. Seizing Soledar would be Russia’s most substantial gain since August, after a series of humiliating retreats in the second half of 2022. Russian forces have been fighting for months to capture Bakhmut. But any victory would come at a massive cost, with troops from both sides having taken heavy losses in some of the most intense combat since Russia invaded Ukraine nearly 11 months ago. The Kyiv government has released photos in recent days purporting to show scores of dead Russian soldiers in muddy fields. The issue of supplying tanks to Ukraine has become the centre of a frenzied round of recent diplomacy, as a number of countries have put pressure on the German chancellor, Olaf Scholz, to allow the supply of Leopard 2s.