Al Jazeera's Sherine Tadros reports on how the north's takeover of Abyei is escalating tensions with the south
At least 15,000 people have fled the southern Sudanese town of Abyei after clashes in the disputed border area, the United Nations has said.
"We have a rough estimate of 15,000 people displaced in and around Agok [in South Sudan]," Elisabeth Byrs, a spokeswoman for the UN Office for the Co-ordination of Humanitarian Affairs said on Tuesday.
Earlier gunmen were reportedly looting properties, days after troops from the government in Khartoum entered the area, while the town of Abyei was set ablaze.
Peacekeepers belonging to UNMIS, the UN mission in Sudan, said on Monday that the burning and looting was perpetrated "by armed elements" but it was not clear whether they were from the north or the south.
Omar-al-Bashir, the Sudanese president, said a "peaceful resolution" for Abyei would be found.
"We are efforting to solve the remaining issues and remove tensions in Abyei," he said in a speech.
Abyei, claimed by both north and south, was due to vote on its future alongside a referendum on independence for the south.
However, it did not hold the poll due to disagreements over who was eligible to vote. On Sunday it was seized by northern troops.
The US special envoy to the country has said Washington would not drop Sudan from a terrorism list if it continued occupying the oil-rich district.
Princeton Lyman said the "occupation" of Abyei by northern troops was "an extremely disproportionate response by the government of Sudan" to an attack on a UN convoy escorting the troops last week.
But Lyman added that there was still hope of the two sides resolving the crisis.
"I am optimistic in this sense: These two entities - Sudan and soon-to-be independent South Sudan - need each other," he told Al Jazeera.
"They have to collaborate for their own good, and while we're now facing a major crisis in Abyei, we're hopeful that the leadership, particularly president al-Bashir [in the north] and vice-president Kiir [in the south] will re-establish the spirit that they talked about ... "
Sudanese government officials in the north said their troops moved into Abyei - inhabited by two tribes backed by the south and north respectively - to drive out the Sudan People's Liberation Army (SPLA), who they said had been occupying Abyei since last December.
The SPLA is the armed force of South Sudan, which held a referendum for independence in January and is due to become an independent state in July.
"As we talk now, there's a very large level of looting and killing," Luka Biong, minister of cabinet affairs, said from Juba.
People in the UN compound had been "slaughtered," he said.
"The most important thing is for [Bashir] to withdraw the Sudan armed forces from the area."
UNMIS strongly condemned the burning and looting in Abyei and called upon the government of Sudan to "urgently ensure that the Sudan Armed Forces fulfil their responsibility and intervene to stop these criminal acts".
Hua Jiang, the chief public information officer for UNMIS, said the burning of property and looting had continued on Monday.
She said Sudanese troops from the north had prevented peacekeepers from conducting their daily, routine patrol.
"We're not able to get out of the compound right now to carry out our duty," she told Al Jazeera from Juba, the capital of South Sudan.
South Sudan also claims Abyei district, which has special status under a 2005 peace deal that ended 22 years of south-north civil war, and has called the occupation "illegal".
The nomadic Misseriya tribe, which is backed by the north, grazes its cattle in Abyei. The Dinka Ng'ok tribe, backed by the south, lives in Abyei year round.