The two African neighbors last Saturday failed to agree on how to withdraw armies from their disputed border after a round of talks, holding back oil exports from landlocked South Sudan through Sudan.
Both countries had agreed in September to set up a demilitarized buffer zone and resume oil production, but neither side has withdrawn its army from the 1,200-mile border.
South Sudan seceded from Sudan in 2011 under a deal that ended decades of civil war. A year ago, South Sudan shut down its entire oil output of 350,000 barrels per day after failing to agree on export and transit fees with Khartoum.
"The government of Sudan's intent to postpone the restart of oil production until the implementation of security arrangements is complete runs counter to the fundamental principles of the (September) accord and continues to undermine the economic and security situation in both states," U.S. State Department spokeswoman Victoria Nuland said in a statement.
Sudan has accused its southern neighbor of backing a rebel group called the Sudan People's Liberation Movement-North (SPLM-North), which still controls part of the Sudan side of the border, complicating the creation of a buffer zone.
The SPLM-North is made up of fighters who sided with the South during the civil war.
Nuland said Sudan should begin direct talks with the SPLM-North in order to bring security to the region, rather than demanding that its security conditions be met prior to further talks.
"Security will only come if Sudan cooperates with South Sudan and begins direct talks with the SPLM-N to address the Two Areas conflict," she said, referring to two disputed Sudan states that border South Sudan.
(Reporting by Anna Yukhananov, editing by Stacey Joyce)