The Security Council passed a resolution by a unanimous vote that calls on Sudan and South Sudan to stop fighting and return to the negotiating table within two weeks.
Tensions escalated last month when forces from South Sudan seized oil fields in Heglig across the ill-defined border separating it from Sudan. Ongoing territorial disputes, ethnic rivalries and conflicts over oil are pushing both sides to the brink of war.
U.S. Ambassador to the United Nations Susan Rice said it was "essential" that both sides return to the negotiating table under the auspices of an African Union peace panel.
"This is ultimately the only way that further conflict can be avoided," she said in a statement.
If both sides refuse, she said, members of the Security Council are "united" in their determination to hold both sides accountable. This may include Chapter VII sanctions, which authorize the use of force.
South Sudan last year gained independence as part of a 2005 agreement that ended one of the bloodiest conflicts since World War II.
"This conflict did not begin last week or last month or even last year," said Rice. "The tensions underlying this conflict have long roots, most recently in the unresolved issues of the comprehensive peace agreement."