The situation in the city of Bakhmut, on the eastern frontline, is becoming "more and more difficult", Ukraine's President Volodymyr Zelensky has said. Russian forces have been trying to take the city for over six months. "The enemy is constantly destroying everything that can be used to protect our positions", Mr Zelensky stated. The Ukrainian leader's remarks came as US Treasury Secretary Janet Yellen warned China against arming Russia during a visit to Kyiv on Monday.