Kiev, June 16 : The UN has warned that thousands of civilians are stuck in Severodonetsk, a key city in Ukraine's Luhansk region where fierce battles are currently raging, with essential supplies running out. All three bridges into Severodonetsk have been destroyed as a result of the fierce battles between Russian and Ukrainian forces, the BBC reported. Capturing Severodonetsk and the nearby city of Lysychansk would give Moscow control of the entire Luhansk region, much of which is already controlled by Russian-backed separatists. Speaking to the BBC, spokesperson for the UN's Humanitarian Affairs office Saviano Abreu said that many of the the stranded civilians were sheltering in bunkers beneath the city's Azot chemical plant. As the last bridge leading out of the city was destroyed earlier this week, it effectively trapping its 12,000 remaining residents inside. "The lack of water and sanitation is a big worry. It's a huge concern for us because people cannot survive for long without water," Abreu told the BBC. He added that food supplies and health provisions were also running out in Severodonetsk. In a social media post, Severodonetsk's Mayor Oleksandr Stryuk said that Ukraine was still in control of the city's eastern district. "Efforts are being made to push the enemy back towards the city centre. It's a permanent situation with partial success and tactical retreat in places," he added. Citing reports, the BBC said that 70 per cent of Severodonetsk is now under Russian control. Earlier, President Volodymyr Zelensky had said that Ukrainian troops in the city were fighting Russian forces for "literally every metre". /IANS