Sudan has withdrawn its support for a United Nations peacekeeping force to replace African Union troops now in the conflict-ridden Darfur region, and is lobbying other countries to discourage the substitution, Jan Pronk, the United Nations envoy for Sudan, said Tuesday. “The government is taking a very strong position against a transition to the U.N., and that is new,” Mr. Pronk said. “Sudan has sent delegations to many countries in the world in order to plead its case: let the A.U. stay and let the U.N. not come.” In another development indicating a snag in the international effort to curb the violence in Darfur, John R. Bolton, the United States ambassador, conceded the failure of the American effort to produce a resolution on a United Nations mission to Sudan by the end of February, a month during which the United States has served as president of the Security Council. Full Story