Sudan has backed down from a warning to the international community not to pledge troops to a U.N. peacekeeping force for Darfur, the U.S. ambassador to the United Nations said Friday. In a letter to several countries earlier this week, Sudan warned that any nation pledging U.N. troops for Darfur was committing a hostile act that was a prelude to an invasion. But Ambassador John Bolton said Sudan s ambassador to Washington and its United Nations envoy told the State Department and the U.N. Security Council president that the letter no longer reflected Khartoum' s policy.