Delegates from South Sudan and Sudan met in Ethiopia this week to settle issues left over from a 2005 peace agreement. South Sudan in July became an independent country under the terms of the 2005 deal.
Oil disputes, ethnic conflicts and fighting along an ill-defined border remain problematic, however.
Top U.N. delegates briefed the U.N. Security Council in a closed-door session. U.S. Ambassador to the United Nations Susan Rice said members were informed that forces from South Sudan and Sudan had pulled out of the disputed border territory of Abyei.
She said she was encouraged by reports from the talks in Ethiopia but viewed the briefings as mixed.
"Many" difficult issues remain unsettled on both sides, she said. Reports of lingering violence and aerial bombardments were doing little to ensure the peace, added Rice.
"It's been not possible for U.N. elements to confirm any of these reports definitively," she said in a statement. "But obviously, what is absolutely clear is that the two sides remain closely poised, in close proximity, and seemingly on a hair trigger."