|US Ambassador Susan Rice arrives in Khartoum as North Sudan gains control of Abyei town. [Reuters]
North Sudan's army appears to have gained control of the main town in Sudan's disputed Abyei region after fierce fighting with the Sudan People's Liberation Army (SPLA), UN and rebel sources said.
UN officials saw 15 tanks of the Sudanese Armed Forces, the northern army, on Saturday in parts of the key town Abyei where earlier mortars slammed against a UN base, Hua Jiang, the UN spokeswoman said.
One of those mortar rounds exploded, but there were no casualties among UN personnel, Jiang said.
"The SAF have entered (the town) Abyei, there is still fighting but they have come with tanks, they are shooting and shooting," Philip Aguer, SPLA spokesman, said.
"Our police have been fighting but the SAF have sent many soldiers in," he added, speaking by phone from Juba, the capital of southern Sudan.
He said northern forces bombed at least four villages on Saturday afternoon in continuation of last week's attacks.
Aguer added that two of the bombed villages were Todach and Tagalei which had been already hit on Friday - a reference to the southern army's allegations that the northern army had begun bombing Abyei that day after previous clashes on Thursday.
Sudanese state television’s news bulletin said the SAF expelled "enemy forces" to the south on Saturday evening.
The violence comes a day after the UN called for an "immediate cessation of hostilities" which has increased in recent days in forms of clashes that include artillery fire.
It also comes a day before a UN Security Council delegation was scheduled to hold talks with the Sudanese government in the country’s capital Khartoum over Abyei.
The armies of North and South Sudan, which is due to claim independence from Khartoum later this year, have accused each other of launching attacks in the region.
Barnaba Benjamin, the information minister of South Sudan, told Al Jazeera that the Sudanese government needed to withdraw its troops.
"The situation in Abyei is very unfortunate and is a deplorable situation, where the president of the republic has ordered the armed forces to invade Abyei militarily and occupy it militarily," he said.
"UN troops should be allowed in the territory until the referendum for them to decide whether to remain with the north or to join the south."
An unnamed diplomatic source on the delegation told the AFP news agency called SAF’s control over Abyei town "a major development".
"Elements of the SPLA have pulled back to the south and are no longer in the town, where about 10 T-55 SAF tanks are patrolling," one official at the United Nations Mission in Sudan (UNMIS), also told AFP.
Fighting in the Abyei region has pitted former civil war enemies against each other since January, when South Sudan voted to become independent in a referendum in January.
It agreed to a peace deal with the north in 2005, but tensions are high in oil-producing Abyei, where both sides have built up forces. The north has said it will not recognise the state unless the south gives up its claim to Abyei.
The US, one of the main backers of Sudan's landmark 2005 peace deal, has deplored the southern forces' May 19 attack on a UN convoy that was lawfully transporting a SAF company.
On Saturday, the White House "condemned" the fresh violence in Abyei and called on the SAF to "immediately cease all offensive operations" and "withdraw its forces" from Abyei.
"Failure to do so could set back the process of normalising relations between Sudan and the United States and inhibit the international community's ability to move forward on issues critical to Sudan's future," the White House said in a statement.