JUBA, Sudan - Armed men burned and looted the flashpoint town of Abyei on Monday after days of violence involving northern and southern troops in the disputed region. Southern Sudan's military said it would defend its territory, while an Arab herdsman said his tribe is in Abyei to stay, an indication Sudan's peace could crumble before the south's July independence.

Violence flared late last week in Abyei, a no man's land between north and south Sudan. Southern Sudan voted in January to secede from the south, and the region becomes an independent country on July 9. But violence in Abyei is overshadowing the march toward independence.

The U.N. mission in Sudan said armed elements were burning and looting in Abyei and said the northern Sudanese Armed Forces must fulfil their responsibility to intervene to "stop these criminal acts."

In photos provided by the U.N., the town appeared deserted except for what appeared to be looters. Some huts appeared to be ablaze; smoke billowed from others. Looters were seen roaming the streets, carrying rifles. Some carried suitcases. Others pulled carts carrying mats, pots and pans, sacks of grain and even bed frames.

Officials in the north indicated that the two sides could be brought back from the brink even as the south said it would respond with force if its territory is breached. A powerful Sudanese Arab tribal chief, meanwhile, said his tribesmen have entered the area with other Arab tribes, and that "Abyei is a northern town."

Both north and south claim Abyei, a fertile region near several large oil fields, and its disputed status has long been recognized as a potential trigger for violence. The ethnic African tribe of the Ngok Dinka and the Arab tribe of Misseriah both lay claim to the area.

Misseriah tribal chief Mukhtar Babu Nimr dismissed the calls and warnings by southerners and the U.N. Security Council, saying that for months the southerners have violated the Abyei protocol and no one complained.

"Abyei was occupied by the southern forces for six months, and there was not a single northern," he said. "No one said anything. Now hours after southerners leave, it is a problem. This is very strange."

Eric Reeves, a professor at Smith College in Massachusetts who has written extensively on Sudan, said Khartoum could use the seizure of Abyei as leverage against Juba on other unresolved north-south issues -- or it could extend the conflict to other oil areas.

"Either will lead to a spread of violence, quite possibly all-out war," he said. "The international community -- and the U.S. in particular -- has very little time in which to convince Khartoum that the costs of this assault will be too great to withstand, and to give peace a second chance."

Civilians fleeing the violence in Abyei are moving farther south -- from the town of Agok toward Turalei -- because of fears of more attacks, said Gustavo Fernandez, an official with medical aid group Medecins Sans Frontieres. Children fleeing the conflict are walking long distances by themselves and risking dehydration during the journey, he said.

A U.N. official in the southern capital of Juba said that U.N. personnel were fired at by members of the southern military while trying to carry out a humanitarian assessment in Agok. A U.N. spokesman declined comment. The U.N. official wasn't authorized to give a name.

Tanks from northern Sudan rolled into the town of Abyei Saturday night, scattering southern troops that were there as part of a joint security unit. The U.N. compound was also hit with mortar fire, and U.N. Secretary-General Ban Ki-moon and the U.N. Security Council called for an immediate end to military action.

The seizure of Abyei followed an attack on a convoy of northern soldiers by southern forces on Thursday and two days of aerial bombardment of the area by the north.

Russia's ambassador to the U.N. told a news conference late Sunday that a Sudanese official had hinted that the government is ready to pull back if guarantees are made that the south won't attack its troops again.

The escalation in violence comes as Southern Sudan, which is predominantly ethnic African, is due to become the world's newest country. The south voted overwhelmingly to secede from the Arab-dominated north in a referendum promised in a 2005 peace deal that ended more than two decades of north-south war.

Southern army spokesman Col. Philip Aguer told a news conference that the south would respond with force if northern troops continue moving south. Aguer said the south would support rebels in Sudan's western region of Darfur and northern militias that support the south in response to the north's actions. He accused the north of using militias to block the south from oil fields.

The northern military "is not only just attacking Abyei, but it's moving for a full-scale war," Aguer said. The south "will not just wait and allow the SAF (Sudanese Armed Forces) to invade Southern Sudan. We have our limits where we are ready to protect our territory."

Under the peace deal, Abyei was also due to have a referendum to decide whether it would remain part of the north or south, but it was cancelled amid disagreements over who was eligible to vote.

Now Abyei town is mostly empty, said Fernandez. MSF staff all evacuated to Agok, to the south, but now citizens and humanitarian aid groups are moving even farther south to Turalei, he said. Tensions among the fleeing populations were high because of fears that violence would arrive in Agok, he said.

The U.N. Security Council, which landed in Juba on Monday, released a statement Sunday blaming both sides for the violence. It said the south had attacked the convoy of northern soldiers and the north had escalated the confrontation by occupying Abyei.

The council demanded "the immediate withdrawal of all military elements from Abyei" and called on both sides to restore calm, uphold the 2005 peace agreement, "and recommit to a negotiated political settlement on the future status of the Abyei area."

The south is mainly animist and Christian and its people are linguistically and ethnically linked to sub-Saharan Africa. The north is overwhelmingly Muslim and many members of the government consider themselves Arabs. Most of Sudan's oil is in the south but the pipeline needed to export it runs through northern territory to a northern-held port.

More than 200 people demonstrated in Juba on Monday against the northern takeover of Abyei. The protesters chanted slogans against Bashir.

"This was a deliberate incursion. They (the north) want to take these actions before July 9 and use them in negotiations," said Erjok Mayor, a rally organizer.