UNITED NATIONS (Reuters) - U.S. Ambassador to the United Nations Nikki Haley said on Monday it was time for the U.N. Security Council to impose  the strongest possible measures  on North Korea over its sixth and largest nuclear test because  enough is enough.   Haley said the incremental sanctions approach of the 15-member council to North Korea since 2006 had not worked and she described North Korean leader Kim Jong Un as  begging for war.    Despite our efforts the North Korea nuclear program is more advanced and more dangerous than ever,  Haley told the council.  War is never something the United States wants. We don t want it now. But our country s patience is not unlimited.  