BBC News with Neil Nunes

One of the Republican party candidates for the US presidential nomination, Rick Santorum, says he will

drop out of

the race, making Mitt Romney the most likely challenger for President Obama in November. Mr Santorum made the announcement in his home state of Pennsylvania with his family at his side. Peter Bowes reports from Washington.

Rick Santorum was barely known around America when he launched his presidential campaign a year ago. The Republican from Pennsylvania positioned himself as the only true conservative in the race. He attacked his opponent and the front-runner Mitt Romney for being out of touch with the needs of ordinary people. But Rick Santorum, who rose quickly in the polls, could not

sustain

his initial popularity. In

suspending

his campaign, he said he would continue to fight for, as he put it, American greatness and the defeat of Barack Obama.

Sudan says its largest oil field Heglig is under the control of the South Sudanese military. South Sudan has acknowledged that its military has advanced to the oil field, but both sides deny starting the fighting. James Copnall is in Khartoum.

Colonel Khalid Sawarmi admitted the Sudanese army had been defeated outside Heglig and had

retreated

to the north. He said his men had not started the battle. A spokesman for South Sudan's armed forces acknowledged his troops advanced to Heglig, but stopped short of claiming control of the oil fields. Colonel Philip Aguer told the BBC his troops were responding to air and ground attacks by the Sudanese armed forces. Heglig is generally considered to be part of Sudan, but South Sudan disputes this.