Correction: An earlier version of this article misstated the date of an attack by southern Sudanese troops on a U.N. convoy escorting Sudanese government troops. The attack occurred May 19, not June 5. This version has been corrected.

President Obama on Thursday voiced “deep concern” over the widening violence in Sudan as his top envoy prepared to travel to the region this month to help resolve a political and military crisis that threatens to upend one of the United States’ principal priorities in Africa: the peaceful division of Sudan into two states.

The White House statement followed Obama’s meeting with his top Sudan envoy, Princeton Lyman. It came as representatives from northern and southern Sudan continued talks Thursday in Addis Ababa, Ethiopia, to try to settle a disagreement over the fate of the disputed region of Abyei, which was attacked by government forces this month in an operation that U.N. officials think might lead to ethnic cleansing.

The Khartoum government and the southern Sudanese People’s Liberation Movement were discussing a deal that would lead to the withdrawal of government troops from Abyei and the deployment of thousands of Ethiopian peacekeepers in the area, according to diplomatic sources familiar with the talks. Meanwhile, fighting has spread in recent weeks to neighboring Blue Nile state and South Kordofan state, where Khartoum’s air force bombarded the area while ground troops and militias sought suspected supporters of the south around the capital of Kadugli.

In recent weeks, senior Obama administration officials have warned Khartoum that its military actions in Abyei, South Kordofan and beyond could undercut the prospects of normalization of U.S. relations with Sudan. On Thursday, the White House said Lyman would press the sides to reach a deal that would lead to a “withdrawal from Abyei and a cessation of hostilities across the region and to support the emergence of two viable states at peace.”

In New York, the United Nations’ top peacekeeping and humanitarian aid officials gave a grim closed-door briefing to the U.N. Security Council on events unfolding in South Kordofan, where more than 60,000 people have fled their homes. The United Nations also cited reports that Sudanese People’s Liberation Army (SPLA) reinforcements may be advancing on Kadugli, raising fears of a resumption of all-out civil war.

“There is a growing sense of panic among some of the displaced population who find themselves trapped by the ongoing violence and ethnic fault lines,” according to a situation report issued by the U.N. emergency relief coordinator this week. After the briefing, Catherine Bragg, the deputy emergency relief coordinator for the United Nations, said that “in the state capital city of Kadugli it is estimated that more than 70 percent of the population have been displaced and many of the 1.4 million residents of the 11 localities where fighting has been reported have been affected.”

Khartoum fought one of Africa’s bloodiest and longest civil wars against the south. The 22-year conflict, which began in 1983, left more than 2 million people dead. The 2005 Comprehensive Peace Agreement, brokered by the George W. Bush administration, formally ended the war and set the stage for southern Sudan to vote on an independence referendum. In January, the south voted to secede from the north, and it is expected to declare independence on July 9.

Although the referendum proceeded with little violence, the two sides remained divided over critical issues: the delineation of the border between the two states; citizenship; water rights; the sharing of oil revenue; and the status of Abyei, which is claimed by the north and south.

Critics of the Khartoum government said the latest military operations in Abyei and South Kordofan were intended to strengthen the government’s hand at the negotiating table. But Sudanese leaders maintain that they have used force only in response to provocation by southern fighters.

The latest flare-up began May 19, when troops from the SPLA opened fire on a U.N. convoy escorting Sudanese government troops in Abyei. The Sudanese army responded with what U.N. officials think was a premeditated military invasion of Abyei, which drove more than 100,000 civilians from their homes around Abyei.

The Washington Post obtained an internal draft report by the U.N. human rights office in Sudan describing the military campaign as “tantamount to ethnic cleansing.” But the United Nations, after a pledge by Khartoum to let civilians return, later revised the text of the report to say that the military campaign might lead to ethnic cleansing if the residents were not allowed to resettle there.

The Sudanese military, meanwhile, has barred the United Nations from the Kadugli airport or from gaining full access to thousands of displaced civilians who have gathered on the outskirts of town and beyond.

“Humanitarian agencies have been able to distribute food . . . and do medical screenings to some of its displaced population,” Bragg said after the council briefing. “However, shortage of water and shelter are a concern for us.”