The South Sudanese government continues to harbour and aid armed groups active in neighbouring Sudan, the United States has said.
Such assistance places South Sudan in violation of a United Nations Security Council resolution as well as numerous agreements between Juba and Khartoum, a State Department spokesman declared.
Aid to Sudanese rebels also violates the internal peace agreement signed last year by President Salva Kiir, the US added.
The US statement indicates that Sudanese armed groups remain involved in conflicts inside South Sudan.
“The presence of Sudanese armed opposition forces in South Sudan, and their involvement in South Sudan’s internal conflicts, destabilises both Sudan and South Sudan,” the State Department said.
“We call on the government of the Republic of South Sudan to ensure Sudanese armed opposition groups are not in a position to conduct armed operations within South Sudan or across the border in Sudan,” the statement says.
Thursday's statement highlights the growing estrangement of Obama administration's from President Kiir's government as well as signs of a reconciliation between Washington and Khartoum.
The State Department said last month that the US “welcomes Sudan's recent efforts to increase counterterrorism cooperation with the United States.”
Sudan's government has sought to prevent the movement of Islamic State members into and through its territory, the US noted.
“Subject to and consistent with US law, we will work cooperatively with the government of Sudan on counterterrorism to enhance the security of both our countries,” the State Department added on September 20.
The US has also lifted sanctions on certain bank transactions involving Sudan, the country's finance minister is reported to have said on October 3.
Removal of sanctions on non-commercial bank transactions will benefit Sudan's humanitarian situation and business environment, Finance Minister Badr el-Din Mahmoud reportedly said.
“This decision will turn a new page,” Turkey's Anadolu news agency quoted the minister as saying in Khartoum.
The US imposed sanctions on Sudan in 1997 as a result of Khartoum's alleged support for international terrorism.
Washington took further punitive steps in 2007 due to the Sudan government's actions in the Darfur region.