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Mr. Obama said the north and the south have a responsibility to end the violence and allow immediate humanitarian access to “desperate people who have been driven from their homes and are now cut off from outside help.”

Valerie Amos, U.N. undersecretary general for humanitarian affairs, said more than 70,000 people have been displaced and many more may have fled from their homes in Southern Kordofan.

“I am … concerned that the overall security situation in Sudan is deteriorating at an alarming rate, with severe humanitarian consequences,” Ms. Amos said in a statement.

Meanwhile, Sudanese President Omar al-Bashir escalated tensions with the south by threatening to block the flow of oil from the south through pipelines in the north if there is no deal on oil revenue sharing before southern independence.

“I give the south three alternatives for the oil. The north is to continue getting its share, or the north gets fees for every barrel that the south sends to Port Sudan,” Gen. Bashir told supporters in Port Sudan on Tuesday.

“If they don’t accept either of these, we’re going to block the pipeline,” he said.

Under the current plan, the north and south split oil revenue 50:50. That amount will change to 70:30 in the south’s favor.

Gen. Bashir has been indicted by the International Criminal Court over alleged war crimes in the western province of Darfur.