While the Sudanese town of Abyei is now empty with its residents having fled the recent violence, the situation there remains tense, according to the United Nations, which called on both sides to cease their hostilities and return to negotiations.

The disputed town, which is contested by both north and south Sudan, has witnessed renewed clashes in recent days, including looting and burning earlier this week, following the takeover of the area by Sudanese Government forces. The violence has led thousands to flee their homes.

"Initial patrols around the area of conflict suggest that looting and pillaging have left the town badly damaged and empty," UN spokesperson Martin Nesirky told reporters in New York, adding that no civilian casualties have been observed and that sporadic gunfire persists in the area.

The recent violence and deteriorating security in Abyei has sparked concern from Secretary-General Ban Ki-moon, who highlighted the situation in his remarks today to the Extraordinary Summit of the African Union on Peace and Security in Africa.

"We must all impress on the parties that military confrontation in Abyei is not an option," Ban told the gathering in Addis Ababa, Ethiopia.

"I have also called on both parties to cease their military operations, withdraw all forces and armed elements from the Abyei Area, and desist from further acts of aggression, including attacks on UN peacekeepers."

Earlier this month, unidentified assailants shot and wounded four peacekeepers serving with the UN Mission in Sudan (UNMIS) while they were on patrol in Abyei, and last week a UN convoy transporting 200 troops of the Joint Integrated Units (JIU) of the Sudan Armed Forces was attacked.

Just yesterday, the crew of four UNMIS helicopters lifting off in quick succession witnessed shots fired from positions believed to be close to the mission's premises in Abyei. The helicopters were not carrying passengers and were not hit, the UN reported.

UNMIS is in the process of deploying an additional company to Abyei to be completed today. Another company of four armoured personnel carriers was redeployed today to the town of Agok, south of Abyei, where most civilians affected by the conflict have fled.

The mission has temporarily relocated some of its civilian staff based in Abyei pending a return to normal security conditions.

Haile Menkerios, the Secretary-General's Special Representative and head of UNMIS, said that the latest developments, particularly the escalation of violence, are a "very drastic setback" amid the progress that has been made by both north and south Sudan.

"What has happened now is a regression to square one… There has to be an immediate cessation of all the fighting and the withdrawal of all troops," he said in an interview with the UNMIS-backed Radio Miraya.

He added that the consequence of the recent military operation has been "disastrous" on the civilian population, noting also that the latest unrest and displacement comes just at the beginning of the rainy season.

UN Humanitarian Coordinator Georg Charpentier has gone to Abyei and to Agok to assess the situation and determine what is needed to alleviate the suffering of the people, hundreds of thousands of whom are estimated to have been displaced.

"UN agencies, with NGOs, are already initiating a plan to assess and to provide services to the humanitarian situation and to provide an assistance to those who have fled Abyei in the area of Agok, and the other areas next to it, and this will allow us to have a clear picture of the numbers of displaced people," said Kouider Zerrouk, a spokesperson for UNMIS.

Deadly clashes have claimed dozens of lives since the start of the year, when a referendum on Abyei's status that was supposed to have been held never took place amid disagreement on voter eligibility. Southern Sudan will formally secede from the rest of the country on 9 July as a result of a separate referendum.