* Emergency declared in Jonglei, Unity states
* Fighting near the flashpoint town of Bor
* Mediator fears fighting could scupper talks in Ethiopia
* White House says will deny support to those responsible (Recasts with state of emergency)
By Carl Odera and Aaron Maasho
JUBA/ADDIS ABABA, Jan 1 (Reuters) - South Sudanese President Salva Kiir declared a state of emergency in two states on Wednesday as his negotiators prepared for peace talks with rebels to end more than two weeks of violence that has pushed the country towards civil war.
Kiir called the emergency in Unity and Jonglei states, the two regions whose capitals are now controlled by rebel forces loyal to former Vice President Riek Machar, who Kiir has accused of plotting a coup.
Gunshots were heard near the presidential palace on Wednesday evening. A presidential spokesman said security forces most likely fired the shots at residents breaking a curfew.
Both sides are under mounting pressure from regional and Western powers to reach a deal to stop the bloodletting that has killed more than 1,000 people in the world's newest state and displaced nearly 200,000 more.
The White House has said it would deny support - vital in a country the size of France that still has hardly any infrastructure more than two years after secession - to any group that seizes power by force.
The rebel delegation earlier arrived in the Ethiopian capital Addis Ababa ready for the ceasefire talks. They said government negotiators had not yet arrived.
Both sides have agreed in principle to a ceasefire but neither has indicated when the fighting would stop and mediators are concerned that fighting around the flashpoint town of Bor will scupper the talks even before they begin.
South Sudan's defence minister earlier said government forces were battling rebel fighters 11 miles (18 km) south of Bor, the capital of Jonglei state, which has untapped oil reserves and was the site of an ethnic massacre in 1991.
"There will have to be a fight because they want to defeat the government forces," Defence Minister Kuol Manyang Juuk told Reuters from the capital Juba, 190 km south of Bor by road.
Rebels loyal to Machar seized control of Bor on Tuesday.
WHITE HOUSE PRESSURE
The Addis Ababa talks will focus on finding ways to roll out and monitor the ceasefire, the East African IGAD bloc that is mediating the talks said.
The clashes, which have spread to half the country's 10 states have unsettled oil markets and raised fears of the conflict spilling over in an already fragile region.
"We don't want to expose the people of South Sudan to a senseless war," South Sudan's Foreign Minister Barnaba Marial Benjamin said on a government Twitter feed on Wednesday.
Kiir has accused his long-term political rival Machar, who he sacked in July, of starting the fighting in a bid to seize power.
Machar has denied the charge, but he has taken to the bush and has acknowledged leading soldiers battling the government.
Clashes between soldiers erupted on Dec. 15 in Juba. The violence quickly spread, dividing the country along the ethnic lines of Machar's Nuer group and Kiir's Dinkas.
South Sudan's neighbours, Washington and the United Nations played a central role in negotiations that ended decades of war with Sudan to the north and led to the secession of South Sudan in 2011, and have been scrambling to stem the latest violence.
The White House upped the pressure for the talks on Tuesday.
"We will hold leaders responsible for the conduct of their forces and work to ensure accountability for atrocities and war crimes," spokeswoman Caitlin Hayden said.
The United Nations Mission in South Sudan said ethnic-based atrocities, often carried out against civilians by uniformed men, had taken place across the country.
Fighting across the country has displaced at least 180,000 people, according to the United Nations.
The clashes have revived memories of the factionalism in the 1990s within the SPLM, the now ruling group that fought Sudan's army in the civil war. Machar led a splinter faction at the time and Nuer fighters loyal to him massacred Dinkas in Bor. (Additional reporting by Drazen Jorgic and Richard Lough in Nairobi, Jeff Mason in Honolulu and Kumerra Gemechu in Addis Ababa; Writing by Drazen Jorgic; Editing by Richard Lough and Alison Williams)