A satellite monitoring project in Sudan backed by actor George Clooney released images Friday that the group said show a military buildup near Sudan's internal north-south border and the destruction of 20 homes.
A medical group said tens of thousands of people have fled.
The new images were released as political leaders from Sudan's north and south and a top U.N. official met in the embattled border zone of Abyei in an attempt to broker peace after a wave of attacks killed more than 100 people.
Fighting broke out in Abyei last Sunday, and southern political leaders blamed the attacks on the north's military. The northern government maintains the southern government is responsible for the clashes due to its failure to remove pro-southern police from the contested area in line with a January agreement.
Abyei is a fertile region that has oil deposits in between north and south Sudan. Southern Sudan voted to secede in January and is slated to become the world's newest nation in July.
But Abyei's future is very much up in the air, and observers worry the region could again erupt in civil war.
The Satellite Sentinel Project released images Friday from Abyei that the group said show a military buildup on both sides of the border. The group said the images appear to show northern Sudanese tanks and artillery within about 60 miles (100 kilometers) of Abyei town, and the "alleged buildup" of southern forces near Lake Abiad since the fall of 2010.
The images, acquired on March 3, were analyzed by the Harvard Humanitarian Initiative. The group said one image shared with The Associated Press shows 20 out of 24 civilian dwellings that have been torched, apparently by arson.
"The intentional destruction of Maker Abior just prior to the resumption of high-level negotiations between North and South demands an unambiguous response from the United States," said John Prendergast of the Sudan advocacy group Enough.
Clooney and Prendergast helped launch the satellite project in concert with the south's January referendum vote. Clooney visited Sudan to help bring attention to what he said is the possibility of a new war.
Prendergast urged the Obama administration to suspend implementation of incentive packages for the north linked to the southern vote.
"Instead, the United States should intensify its peace efforts," he said.
The medical aid group Medicins Sans Frontieres said Friday that tens of thousands of people have fled Abyei since Thursday, "leaving it mostly empty."
The U.N. said it was a "matter of urgency" that Friday's meeting take place.
"The purpose of this meeting is to try to stop the current violence and also allow the migration to take place, to proceed," said U.N. spokeswoman Hua Jiang, referring to the yearly migration of the Arab cattle-herding Misseriya people, whose seasonal grazing through the fertile region has been delayed this year due to insecurity in Abyei.
The violence could undermine negotiations that took place between north and south Sudan in Ethiopia this week, said Zach Vertin of the International Crisis Group. The violence could harden positions among Abyei communities, "thus making it more difficult to sell any future agreement on the ground," he said.
The U.N. delegation was led by Haile Menkerios, head of the billion-dollar-per-year U.N. peacekeeping mission in Sudan. The governor of Southern Kordofan state, Ahmed Haroun, also attended. Haroun is wanted by the International Criminal Court in The Hague on charges of war crimes for his role in the ongoing conflict in the western region of Darfur.
The top official in Abyei, Deng Arop Kuol, told the AP on Thursday that the northern military participated in the Wednesday attack that killed scores of police who attempted to defend a police post in Maker Abyior that came under attack from Misseriya militia forces.
These claims have not been independently verified, and Kuol said Friday that insecurity is preventing U.N. peacekeepers in Abyei from visiting the sites of the attacks.
An internal security report by the U.N. and seen by the AP estimated that "about 20,000 to 25,000 people" _ about half the population of Abyei _ may have left.
Following violence in early January in Abyei, the U.N. helped broker an agreement to allow the Misseriya to migrate with their cattle and to enable the safe passage of tens of thousands of southerners streaming home from northern Sudan. The agreement has not been implemented.
Abyei had been promised its own self-determination vote in the 2005 north-south peace deal that ended decades of civil war, but disputes between the political leaders from north and south prevented the Abyei referendum from happening.
"What makes Abyei so particularly dangerous is that we don't know what Khartoum's motives are," said Eric Reeves, a professor at Smith College in Massachusetts who has written extensively on Sudan.
"Do recent actions represent a pretext for war? Are they an extension of the brinksmanship that has defined the regime's strategy in extracting international concessions? Either way, only Khartoum benefits from present turmoil in Abyei, certainly not Juba."
Associated Press reporter Jason Straziuso in Nairobi, Kenya contributed to this report.