Ukrainian forces are holding out against Russia in the southern port city of Mariupol, officials say, despite some reports suggesting the battle was nearing its end. Deputy mayor Serhiy Orlov told the AFP that "battles for Mariupol continue". He also denied reports about a marine brigade which posted to Facebook about running out of ammunition and facing a "last battle". "The information about the marines is fake. I don't comment on fakes." "The Russians temporarily occupied part of the city. Ukrainian soldiers continue defending the central and southern parts of the city, as well as industrial areas and so on," Mr Orlov said. In a Facebook post, Ukrainian armed forces Commander-in-Chief Valerii Zaluzhnyi said the military still had stable, open lines of communication with its soldiers inside the city. The military is doing "the possible and impossible" to save lives and fight against Russian forces, he wrote. Mariupol lies between the pro-Russia breakaway regions of Donetsk and Luhansk in the east, and annexed Crimea in the south. Seizing the city has been a major goal of the Russian offensive. Western officials are warning that this is an "incredibly important window" for vital support to Ukraine, as Russia prepares to double or triple the number of troops it has in the country's eastern Donbas region. In briefings, officials say Russia is re-equipping its combat units and adding fresh troops - which will take time. In the meantime, Western economic and military aid for Ukraine could prove valuable in preparing for any renewed offensive. Meanwhile, Ukraine's President Volodymyr Zelensky said that tens of thousands of people had likely been killed in Mariupol. The AFP has not verified the figure, but reports from the region and the refugees fleeing the city spoke of bodies lying in the streets and most buildings damaged or destroyed.