An international monitoring group says north Sudan's occupation of the contested Abyei region was likely a "premeditated and well-planned" operation.
The Satellite Sentinel Project, which uses satellite photos to observe developments in Sudan, says it documented a build-up of tanks, helicopters, and troops along roads near Abyei in the weeks before Saturday's occupation.
Nathaniel Raymond is director of operations at the Harvard Humanitarian Initiative for the satellite Sentinel Project. To hear his interview with VOA's Joe De Capua on the latest images over Abyei, click below.
The project also says it has collected documentary evidence of possible war crimes and crimes against humanity in Abyei.
Witnesses have reported burning and looting of buildings in Abyei since northern forces seized the oil-rich area, which is claimed by both north Sudan and the soon-to-be-independent south.
The United Nations says more than 15,000 people have fled southward to escape the violence.
In a speech Tuesday, Sudan's President Omar al-Bashir said the north will not withdraw from Abyei, which he described as "northern Sudanese land".
The fighting in Abyei has raised fears of a new civil war in Sudan. The north and south fought for 21 years before signing a peace agreement in 2005.
South Sudan voted to split from the north in a January referendum.
Southern leaders say the north occupied Abyei to provoke war and derail secession. The north says it acted to prevent the south from annexing Abyei by force.
North Sudan blames the south's Sudan People's Liberation Army for an attack on northern troops in Abyei last week that killed at least 22 soldiers. The Bashir government says dozens more are missing.
The north and south had been conducting joint patrols of Abyei while trying to negotiate the region's future.
A planned referendum on whether Abyei should join the north or south was cancelled because the sides could not agree on who would be eligible to vote.