UNITED NATIONS (Reuters) - Russia s U.N. Ambassador Vassily Nebenzia called on North Korea on Wednesday to stop its missile and nuclear tests and for the United States and South Korea not to hold military drills in December as it would  inflame an already explosive situation.   We strongly call on all concerned parties to stop this spiral of tension,  he told the U.N. Security Council.  It is essential to take a step back and weigh the consequences of each move.  