Salva Kiir, the South Sudan leader, has called on the Khartoum government to withdraw its troops from the Abyei region but stressed he had no intention of going to war with the North.
"We will not go back to war, it will not happen," Kiir said on Thursday in his first public statement since northern troops took over Abyei last week. "We are committed to peace."
Sudanese forces and South Sudan separatist fighters fought for decades before a 2005 peace deal that also allowed southerners to vote overwhelmingly for independence in a referendum in January.
But Abyei, an oil-rich region lying on the border claimed by both north and south, was exempted from the January referendum amid arguments as to who was eligible to vote.
On Saturday northern troops and tanks overran Abyei town, the main settlement in a fertile border district, sparking an international outcry and forcing thousands to flee.
Four United Nations helicopters were shot at and agencies have been looted, a UN spokeswoman said, in what looks like an act by the militias allegedly backed by North Sudan.
More than 10,000 of Abyei's residents - mainly southern supporting Dinka Ngok people - have fled the fighting across the border into the south, according to the UN. Up to 30,000 more have fled southern border areas.
"We fought enough. We made peace," said Kiir, who is also the first vice president of united Sudan.
He directly urged Omar al-Bashir, Sudan's president, to withdraw his troops despite al-Bashir's refusal on Tuesday to do so.
"I am calling upon my president to pull out his forces from Abyei," Kiir said, saying that the conflict sparked by a shooting incident last Thursday was "an over-reaction from my brother in the north".
But Kiir reassured the people of Abyei - who the south believes should be part of their nation-to-be - that northern soldiers would leave.
"The people now occupying [Abyei] are invaders and they will go out," he said.
Warning against violence
Kiir also warned Khartoum against any further violence, saying that the north "will have to do it while the world will see them".
He said that the recent fighting would not stop the south from being recognised as an independent state in July.
"The South will become independent on July 9, whether the north recognises the south or not," the southern leader said.
Barnaba Marial Benjamin, the Southern information minister said that northern-supporting Misseriya tribesmen were moving into the Abyei area to replace them.
"Thousands of Misseriya are coming into Abyei, while the Ngok Dinka people who live there flee south from the attacks," he said.
Misseriya leaders have denied the claims, but that UN said on Wednesday that gunmen that appeared to be a Misseriya militia were seen moving towards the southern border.
The Sudanese president has rejected international calls to pull his troops out of Abyei.
But in a scaling back of rhetoric, Khartoum's ruling National Congress Party (NCP) said there was "no intention of going back to war," the official SUNA news agency said late on Wednesday.
Al-Hajj Adam Yusuf, a senior NCP member, said the party is "committed" to the 2005 peace deal.