JUBA South Sudan's army said there were no orders to withdraw from the border with Sudan to set up a buffer zone by a deadline on Monday, despite the government saying last month it had begun pulling back its troops.
In turn, Sudan said South Sudan's army was occupying territory north of the border, violating a peace deal brokered by the African Union in September.
The statements seems to be just the latest example of mistrust between the two countries that came close to war in April in the worst border clashes since South Sudan seceded in 2011 under a deal that ended one of Africa's longest civil wars.
The African Union brokered the deal to defuse hostilities. But the nations have failed set up a buffer border zone and resume oil exports from the landlocked South Sudan through Sudanese pipelines, as they had agreed.
The buffer zone is a pre-condition for Sudan to allow oil exports - vital to both countries' beleaguered economies - to restart. Juba shut down its output of 350,000 barrels day a year ago in a row with Khartoum over pipeline fees.
In a sign of goodwill, South Sudan said three weeks ago it had started to unilaterally withdraw its troops from the border and would set up its side of the 10 km (6 mile) buffer zone by Feb 4.
But South Sudan's military spokesman Philip Aguer told Reuters on Monday the army had not even started to pull out from the border, despite the government statement.
"There are no orders to withdraw and I don't think there will be any unless there is an agreement from both governments," Aguer said. "We will never withdraw unless there is an agreement for a timely withdrawal for both armies."
Sudan's army spokesman al-Sawarmi Khalid accused South Sudan of occupying six areas inside Sudan, which he called a clear violation of September's deal, state news agency SUNA said.
"This is having a grave impact on the joint interests of the two peoples," Sawarmi said.
He said Sudan had informed the U.N. peacekeeping force, which will monitor the buffer zone once it is operational, that it had no armed forces south of the planned zone.
It was not possible to verify that because Sudan has so far not announced any withdrawal, while both sides often use different maps to claim territories along the almost 2,000 km long border.
The African Union twice brought together Sudan's President Omar Hassan al-Bashir and his South Sudanese counterpart Salva Kiir in Ethiopia last month to end the stalemate but there has been no sign of progress.
Over the weekend Juba accused Khartoum of killing a South Sudanese soldier in two air attacks on their border. Sudan denied the allegation. Reuters reporters have witnessed Sudanese air attacks on southern territory in the past.
(Reporting by Hereward Holland, Khalid Abdelaziz and Ulf Laessing; Editing by Alison Williams)