Sudanese President Omar al-Bashir has suspended an upcoming summit with South Sudan following a series of fresh clashes between the two countries on Monday.

President Bashir had been set to travel to Juba on April 3 to discuss disputes about oil revenues and border issues with his South Sudanese counterpart, Salva Kiir.

But Sudan's state radio said Monday that Mr. Bashir was suspending the trip after his government accused the south of attacking the oil-rich border region of Heglig, which is claimed by both countries.

South Sudan blamed the clashes on Sudan, saying Khartoum used warplanes and ground troops to attack several of its positions along the tense, disputed border. Both sides claimed they were acting in self-defense and declared victory following the fighting.

U.N. Secretary-General Ban Ki-moon said Monday he is “deeply concerned” about the clashes, and urged both sides to “peacefully address their differences.” He also urged Mr. Kiir and Mr. Bashir to continue with the proposed April talks.

Since South Sudan's independence in July, the two neighbors have not been able to agree on the demarcation of their 1,800 kilometer border or how much South Sudan should pay to export oil through Sudan.

The south took over most Sudanese oil production but is refusing to pay what it considers excessive transit fees to use northern pipelines. The landlocked south needs the pipelines to send the oil to international markets.

The dispute prompted South Sudan to shut down all oil production, a move analysts say is likely to hurt both countries financially.

The sides are also in disagreement over the status of southerners living in the north, and regularly accuse each other of supporting the other's rebel groups.

South Sudan gained independence from Sudan last July.