The head of Russia's Wagner mercenary group, which is spearheading the longest battle of Moscow's intervention in Ukraine, has complained his forces still lack ammunition, blaming possible "betrayal."Kremlin ally Yevgeny Prigozhin, whose recruits have been fighting for months to capture the battle-scarred city of Bakhmut, has been entangled in a power struggle with the Defense Ministry and accused them of withholding supplies.In a post on social media late on Sunday, Prigozhin complained that Russian reservists meant to deploy to Bakhmut had been diverted and that ammunition promised by the military was days late in arriving."We are trying to understand what the reasons are — the usual bureaucracy or betrayal," Prigozhin said in reference to the deliveries of ammunition.Bakhmut has become the bloodiest and longest-running battle of Russia's year-long intervention in Ukraine, even though analysts suggest the city holds little strategic significance.Observers say that both sides are trying to exhaust each other to limit their opponent's ability to mount any further offensive in the coming months.With Russian forces reporting gains to encircle the city, the U.S.-based Institute for the Study of War has said Ukrainian forces may have initiated a strategic retreat from the city."Ukrainian forces are likely conducting a limited tactical withdrawal in Bakhmut, although it is still too early to assess Ukrainian intentions concerning a complete withdrawal from the city," it said in an analytical note.Prigozhin warned over the weekend that if personnel and ammunition shortages became sufficiently acute, his forces would be unable to hold captured territory and that this could bring about a collapse in the front."If Wagner retreats from Bakhmut now, then the entire front will crumble," he said in another post.The Kremlin claimed last year to have annexed the eastern Donetsk region of Ukraine where Bakhmut is located and has made its complete capture its military priority.