By Andrea Shalal WASHINGTON (Reuters) -The United States and its allies will impose “severe sanctions” on Russia after its military forces launched an attack on Ukraine, U.S. President Joe Biden said after blasts were heard in the Ukrainian capital of Kyiv and other cities. Biden said he spoke with Ukrainian President Volodymyr Zelenskiy and briefed him on the steps Washington was taking to rally international condemnation of Russia, including at a special meeting of the United Nations Security Council. “Tomorrow, I will be meeting with the leaders of the G7, and the United States and our alli…