Omar al-Bashir, Sudan's president, has said he will order the flow of oil from South Sudan to be cut off if it backs rebels in the insurgency-hit Sudanese states of South Kordofan and Darfur.
He said on Monday he would "completely close the pipeline" that carries oil from South Sudan to ports on Sudan's Red Sea coast.
"We warn the government in the South that if they provide any assistance to the Sudan People's Liberation Movement-North (SPLM-N) or to the rebels in Darfur, we will completely close the pipeline," Bashir said.
"We will know if they stop the assistance, and we will know if they assist them."
Bashir was speaking at a ceremony after the army recaptured Abu Kershola town in the far north of oil-rich South Kordofan, which rebels seized a month ago.
Claims and denials
Sudan accuses South Sudan of backing rebels fighting in South Kordofan and Blue Nile as well as in Darfur - claims which South Sudan denies.
Rebels of the Sudan Revolutionary Front coalition seized the town of Abu Kershola on April 27 during attacks on several nearby areas in South Kordofan.
Its recapture was recently announced by Mohammed Hussein, Sudanese defence minister, and confirmed by the rebels who said they pulled back for "humanitarian reasons".
Gibril Adam, a spokesman for the rebels, said the fighters pulled out of Abu Kershola to ease a Khartoum government blockade on the town that was taking its toll on residents there.
In March Sudan and South Sudan, which split from Sudan in July 2011, signed detailed timetables to resume the flow of South Sudan oil through a major pipeline in the north that runs to a port on the Red Sea.
Eight other pacts to normalise relations were signed.
Bashir said in his speech on Monday that all of the nine agreements must be respected.
"Failure to abide by any agreement will nullify the nine accords," he said.
Billions in revenue
Bashir's remarks come less than a month after his government announced that South Sudanese petroleum had returned to Sudan's main Heglig facility.
Heglig, along the disputed border with South Sudan, is where the export pipeline begins a journey of about 1,500km to the Port Sudan terminal on the Red Sea.
The pipeline will carry oil that will bring billions of dollars in revenue to both countries once exports resume.
Harriet Martin, reporting for Al Jazeera from Khartoum on Tuesday, said: "One of the problems now is how President [Salva] Kiir [of South Sudan] is going to handle [Bashir's warning]."
She said Kiir has previously faced accusations of backing the rebels, most of them former allies of the SPLA which for decades waged an armed rebellion against Khartoum until a ceasefire was signed in 2005, paving the way for the south to secede.