Updated

Seventy northern Sudanese troops were killed and more than 120 are missing from an attack last week by southern Sudanese forces near the disputed region of Abyei, a Sudanese diplomat said Tuesday, describing a toll that if verified marks one of the bloodiest clashes since the end of Sudan's civil war.

The south voted to secede from Sudan, Africa's largest country, this year but the future of the 4,000-square-mile (10,500-square-kilometer) Abyei region, which lies near the north-south border, was left in doubt. The fighting that began last Thursday threatens to unravel a 2005 peace deal and re-ignite a civil war that left more than 2 million people dead.

According to the U.N., southern troops started the clash Thursday by attacking a column of northern troops and U.N. troops peacekeepers who moving away from Abyei. The U.N. condemned the attack. A U.N. spokeswoman, Hua Jiang, said Tuesday that no U.N. troops were killed.

Kamal Ismail Saeed, Sudan's ambassador to Kenya, told a news conference in Nairobi that 197 northern troops were killed or missing after the southern attack. A more detailed statement from his embassy said 70 troops were killed and more than 120 others missing.

Saeed said the attack caused the Sudanese Armed Forces, or SAF, to respond.

"I think that was a serious blow which ended the continuous patience and self restraint of SAF, so it responded in self defense," Saeed said.

Northern troops have moved south through Abyei, sending thousands of civilians fleeing. Buildings in the region's main town, also called Abyei, have been torched. The U.N. estimated on Tuesday that 25,000 to 30,000 have fled.

The U.N. mission in Sudan said gunmen were burning and looting in Abyei town on Monday and called on the Sudanese Armed Forces to intervene to "stop these criminal acts." In photos provided by the U.N., some huts appeared to be ablaze and smoke billowed from others as rifle-toting looters roamed the streets. Some pulled carts carrying mats, pots and pans, sacks of grain and even bed frames.

Col. Philip Aguer, a spokesman for the southern military, said Tuesday that northern troops remain north of a river seen as the dividing line between north and south, but he warned that if they cross over that would constitute a violation that the south "cannot tolerate."

Both north and south claim Abyei, a fertile region that's almost the size of Connecticut and is located near several large oil fields. The south voted in January to secede from the north in a referendum promised in a 2005 peace deal that ended more than two decades of north-south civil war.

A referendum on Abyei's future was supposed to have been held simultaneously, but the two sides could never agree on who was eligble to vote, and Abyei's referendum wasn't held. The ethnic African tribe of the Ngok Dinka, which is mostly southern-based, and the Arab tribe of Misseriah both lay claim to the area.

"What has transpired is a grave risk to peace and stability," said Susan Rice, the U.S. ambassador to the U.N. She called the seizure of Abyei a "serious violation" of the peace agreement.

Saeed said that Khartoum remains committed to avoiding a new war. But Eddie Thomas, an analyst with the Rift Valley Institute who studies Sudan, said that some people in the Sudanese capital of Khartoum are saying that "the war has started already."

Thomas called the latest violence a "very serious departure" from the often volatile but functioning relationship between Sudan's north and south.

Over 1,400 people have been killed in South Sudan so far this year already — more than in the whole of 2010 — and at least 117,000 have fled their homes as violence has dramatically increased in recent months, the British charity Oxfam said.

Thousands of residents have fled south from Abyei out of fear of violence, and aid groups have relocated south of Abyei.

Residents in the southern army-held town of Agok, which lies on the southern edge of the Abyei region, are fearful of attacks. U.N. officials and aid group staff in Agok told The Associated Press by phone that intermittent artillery fire has been heard in the distance since Sunday.

The south is scheduled to become an independent nation on July 9.

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Straziuso reported from Nairobi, Kenya.