Sudan accused South Sudan of having supported rebels who launched a major assault two weeks ago, warning this could derail recent oil and security agreements between the African neighbours, state media said on Saturday.
The two countries agreed in March to resume cross-border oil flows and end tension that has plagued them since South Sudan's secession in 2011.
Since then ties have improved with Sudan receiving last week the first oil exports from the landlocked South, which had shut down its production in January 2012 in a dispute over pipeline fees.
But in a new setback, Sudan's National Intelligence and Security Services (NISS) said South Sudan had helped rebels who two weeks ago attacked the central city of Um Rawaba. It was the worst assault since a raid on Khartoum in 2008.
"The support for the (rebel) forces ... included fuel supplies and the opening of military hospitals in the South to receive wounded Sudanese rebels," SUNA said, quoting NISS.
South Sudan also had recently supported rebels from the western region of Darfur and two border states with vehicles, SUNA said, adding South Sudan also has provided weapons, ammunition and training at several camps in its Unity state to form a "another force" to send into Sudan.
"NISS has confirmed that Juba has supported rebels against Khartoum since the cooperation agreement (to resume oil flows)," SUNA said.
South Sudan also had issued emergency travel documents for wounded rebels to receive medical treatment in some African countries and hosted some of their leaders in the capital Juba, SUNA said.
The security services "urged the South's government to stop any involvement in support of Sudanese rebels which threatens the implementation of all cooperation deals between Khartoum and Juba," SUNA said.
There was no immediate comment from Juba, which has long denied it was supporting rebels on Sudanese territory.
Khartoum had since the March deal stopped accusing Juba of backing any rebels but mistrust runs deep between the two sides, which fought one of Africa's longest civil wars before a 2005 peace deal.
The Um Rawaba attack, a normally placid commercial hub, was conducted by an alliance of three rebel groups from Darfur, scene of a decade-long rebellion of non-Arab tribes, and the Sudan People's Liberation Movement-North (SPLM-North).
The SPLM-North is made up of fighters who sided with the south during civil war and ended up with southern secession in Sudan. They complain like the Darfur rebels of marginalisation in a country controlled by an Arab elite in Khartoum.
Sudan and South Sudan came close to war in April 2012 when border skirmishes broke out over oil exports fees, rebel support and disputed territory.
Under international pressure, both agreed in March to set up a buffer zone on both sides of their border, a condition for Sudan to allow through South Sudan's oil exports.