Sudan's president threatened to block pipelines in the south if the government there doesn't pay to transit oil or share it with Khartoum, the official news agency reported Wednesday.
Southern Sudan voted overwhelmingly in January to secede from Sudan and become an independent country in July. That vote was part of a 2005 peace deal that ended more than two decades of war.
The two governments are still negotiating how oil wealth will be shared between the north and the south.
President Omar al-Bashir's comments late Tuesday in the port city of Port Sudan seem to be hardening his side's negotiating position, particularly in the context of borders clashes.
Al-Bashir said the southerners "have one of three options: either we share the oil, or they pay fees and taxes for every single barrel that passes through the north or we will shut down the pipeline," according to Sudan's official news agency.
Relations between the two partners remained rocky throughout the transitional period, and tension has increased since the vote. Oil is at the center of the fraught relations, as most of it lies in the south, but all the pipelines and the transporting port are in the north.
The south, which does not have any refineries of its own, relies on oil for more than 95 percent of its budget.
Even so, al-Bashir said his country still wants good relations with the south.
Troops from northern Sudan moved into the disputed central Abyei region last month, sending tens of thousands of people who are aligned with the south fleeing.
After regional mediation, the two sides signed an agreement Monday to demilitarize the area.
President Barack Obama urged north and south Sudan to agree to an immediate cease-fire in the state of South Kordofan. In a statement, he praised an agreement to allow Ethiopian peacekeepers into the contested Abyei area.
The U.S. says Sudanese forces have shelled and bombed the area and that there are reports that forces aligned with the government are arresting and allegedly executing southern Sudanese forces and sympathizers.
Obama said reports of attacks based on ethnicity were "deeply disturbing."