African Union mediator Thabo Mbeki urged the UN Security Council to take action to stop the fighting between Sudan and South Sudan, warning that both sides are locked in a "logic of war" with hardliners increasingly in control.
Security Council members promised to urgently discuss how to address the crisis, including the possibility of sanctions, said US Ambassador Susan Rice, the current Security Council president.
She briefed reporters about the former South African president's closed discussion with the council via videoconference.
Mr Mbeki, along with Haile Menkerios, a special UN representative to Sudan, "described a disturbing situation in which both sides are locked in, and I quote, 'a logic of war'," Ms Rice said.
"They stressed that hardliners are winning the day in both Juba and Khartoum and urged the Security Council to engage with both governments directly to convince them to walk back their positions."
A border conflict between Sudan and South Sudan escalated when the South seized the disputed oil town of Heglig. Sudan has responded with fierce aerial bombardment of the town.
The fighting is the bloodiest since South Sudan broke away from Sudan last July and became the world's newest nation. The crisis threatens to widen into all-out war.
Ms Rice said Mr Mbeki told the council that Khartoum believes South Sudan is seeking regime change in its northern neighbour "and that if that is the case, then the objective of Khartoum would also be regime change" in the South.
"Frankly, one would hope that that is rhetoric and not the objective or the purported objective of either side," Ms Rice said.
She said Security Council members reiterated their demands that the South's forces withdraw from Heglig and that the Sudanese armed forces end their bombardment.
She provided no details on the sanctions the council might consider.
In Luxembourg, UN Secretary-General Ban Ki-moon also called "on both parties to end the fighting immediately and to respect international humanitarian law and the protection of civilians".
The ambassadors of South Sudan and Sudan each described their countries as the victim.
South Sudan's UN ambassador, Agnes Oswaha, insisted that her country "took Heglig out of self-defence and also because the Sudan army has been using the area as their operation base to wage their attacks on the Republic of South Sudan.
"We have reiterated our position over and over calling upon Khartoum to return to the negotiation table," Ms Oswaha told reporters after Mr Mbeki's briefing. "Our intention is not regime change."
Sudan's UN Ambassador Daffa-Alla Elhag Ali Osman, said any sanctions the Security Council discusses should be directed at South Sudan because of its seizure of Heglig.
"We are not an aggressor. We are the victim," he said, adding that Sudan would return to talks when the government of South Sudan "returns to its senses and accepts a withdrawal".
The fighting has displaced more than 100,000 people.