The United States and the United Nations have expressed concern about the escalating hostilities between Sudan and South Sudan and have called for immediate cessation of hostilities.

U.N. chief Ban Ki-moon urged South Sudan's president, Salva Kiir, Wednesday to consider holding a presidential summit to build confidence and assure the people in Sudan and South Sudan that peace and dialogue are the only option for both sides.

A spokeswoman for the U.S. State Department, Victoria Nuland, says the United States condemns military involvement on both sides. She called on Sudan and South Sudan to withdraw all forces deployed across the border, which they both recognized in a 2005 peace agreement.

The warnings come after Sudan Wednesday announced that it is pulling out of talks with South Sudan, after South Sudan's army claimed control of the oil-producing town of Heglig in a disputed border region.

In an interview with VOA , Sudan's deputy foreign minister, Ramatallah Mohammed Osman, accused the south of aggression.

He said he does not think that in this situation there will be talks. He questioned how it is possible to talk with people who have occupied your land.

Osman also called for the troops' quick removal.

“But now we ask the international community to exert pressure on the government of South Sudan to withdraw its forces immediately from this part of Sudan.”

Sudan is accusing South Sudan of launching attacks in Heglig and surrounding areas with the help of local rebels who have been fighting Khartoum since June of last year. The south says it pursued Sudanese troops into Heglig after repulsing an attack Tuesday.

The African Union issued a statement Wednesday urging both sides to respect each other's territorial integrity. It also called on the south to remove its troops from Heglig.

The AU is trying to mediate bitter disputes between the two Sudans stemming from the south's independence last year. But the talks in Ethiopia's capital have made little progress.

Key issues include borders, the sharing of oil revenue and the status of nationals in each other's territory.

Both countries have suggested the possibility of renewed war. Before their separation, north and south Sudan fought a 21-year civil war that ended with the 2005 peace agreement.

The two men were scheduled to meet last week, but the summit was cancelled because of an earlier round of fighting over Heglig.

A U.N. spokesperson said the secretary-general has discussed the situation with the Ethiopian prime minister and is likely to speak to other regional leaders.