By Dmitry Antonov, Tom Balmforth and Simon Lewis MOSCOW/WASHINGTON (Reuters) -Russia said on Thursday it was clear the United States was not willing to address its main security concerns in their standoff over Ukraine, but both sides kept the door open to further dialogue. The United States and NATO submitted written responses on Wednesday to Russia’s demands for a redrawing of post-Cold War security arrangements in Europe since it massed troops near Ukraine, prompting Western fears of an invasion and new U.S. pledges of defense support. Kremlin spokesman Dmitry Peskov said Moscow needed time …