US President Barack Obama said on Monday that the "killing of innocents" must end in Sudan and South Sudan, after weeks of border fighting in contested regions and tension between the two states.

US President Barack Obama said on Monday that the "killing of innocents" must end in Sudan and South Sudan, after weeks of border fighting in contested regions and tension between the two states, AFP reported.

"In Darfur, Abyei, South Kordofan and the Blue Nile, the killing of innocents must come to an end. The presidents of Sudan and South Sudan must have the courage to negotiate because the people of Sudan and South Sudan deserve peace," Obama said at the US Holocaust Museum in Washington.

Washington had earlier condemned a Sudanese air raid on South Sudan and urged an "immediate" halt to hostilities and a return to talks.

The United States on Monday condemned a Sudanese air raid on South Sudan and urged an "immediate" halt to hostilities and a return to talks, the State Department said.

Early on Monday, Sudanese warplanes carried out an intensive bombardment of the Unity state capital town of Bentiu and neighboring Rubkotna, Sudan Tribune, Sudan Tribune reported.

Bombs fell on a key bridge and a market in the state capital of Bentiu, where large plumes of grey smoke rose high into the air, as screaming civilians ran in panic. The incident prompted heavy gunfire from Southern soldiers hoping to shoot down Khartoum's warplanes.

The US State Department spokeswoman Victoria Nuland said in a statement
Monday that Washington recognized South Sudan's right to self-defense and urged it to exercise restraint in its reaction to Sudan's attack in Unity State, "and to refrain from disproportionate actions which would only further enflame the hostilities between the parties."

Border clashes between Sudan and South Sudan have escalated with waves of air strikes hitting the South, and Juba seizing the Heglig oil hub on April 10.

Since the invasion, production at Heglig has been shut and facilities there are leaking.

The Heglig violence was the worst since South Sudan won independence in July after a 1983-2005 civil war, in which some two million people died.