(CNN) -- As warring sides prepared to hold their first face-to-face talks to end weeks of ethnic fighting in the world's newest country, clashes flared around a key town Sunday.
Nhial Majak Nhial, the mayor of Bor, told CNN that rebel troops had been driven away from his town, which has exchanged hands several times during three weeks of violence that has killed hundreds and forced about 200,000 people from their homes.
Defense Minister Kuol Manyang said government forces tried to take back the disputed town but were forced to retreat to a military base eight miles away after rebels ambushed them.
Brig. Gen. Abraham Jongroor was killed and several officers were wounded when rebels attacked, the defense minister said.
Helicopters airlifted dozens of injured government troops to a military hospital in Juba, about 125 miles (200 kilometers) away.
Bor, capital of the oil-rich Jonglei state, has been the scene of some of the heaviest fighting during the violence, as military forces have battled the rebel fighters.
"Their technique of fighting is numbers -- they are using numbers against capable and well-trained government troops," Nhial said. "Many of their men, some even children, have died."
President Salva Kiir and the rebels' leader, former Vice President Riek Machar, have sent delegations to the Ethiopian capital, Addis Ababa, for talks to thrash out a ceasefire.
Face-to-face negotiations were scheduled to begin on Sunday but now are expected to start Monday morning, said Mahboub Maalim, executive secretary of the Intergovernmental Authority on Development, a regional group mediating the talks.
Mediators meet both sides
While neither Kiir nor Machar are in Addis Ababa, home of the African Union, group representatives have gathered and are talking amongst themselves on the sidelines, Maalim said.
"A lot of discussing and discussions going on for sure... we are ready to start face-to-face anytime, but we have to wait on the groups to be ready," he said.
The talks will focus on the cessation of hostilities and negative propaganda, the granting of access to monitors and to humanitarian aid workers, and the question of detainees, Maalim said on Saturday.
The proxy talks have been attended by special envoys to IGAD; the heads of negotiating teams of the two South Sudanese parties; Maalim; and the ministers of foreign affairs of Ethiopia and Kenya.
No breakthrough has come yet despite pressure on Kiir and Machar from African and Western powers to end the conflict. So far, the mediators met with representatives of both delegations to try to pin down the issues and set out a framework for the talks.
Speaking during a visit to Israel, U.S. Secretary of State John Kerry said the negotiations needed to be "serious."
"They cannot be a delay gimmick in order to continue the fighting and try to find advantage on the ground at the expense of the people of South Sudan," he said. "We will work to apply international pressure to any elements that attempt to use force to seize power. That is not acceptable."
But as the two sides' teams negotiate, fighting has continued in their country.
So far the violence has claimed more than 1,000 lives and displaced about 200,000 others.
Humanitarian agencies have warned that the estimated 200,000 who have fled to makeshift camps are facing dire conditions, with many lacking clean water and sanitation in makeshift camps.
The fighting began in Juba on December 15 but quickly spread across the country, with reports of mass killings soon emerging.
Kiir, from the Dinka ethnic group, accused troops loyal to Machar, from the Nuer community, of trying to launch a coup. The two have long been political rivals, and Kiir dismissed Machar, along with the Cabinet, in July.
Although the conflict began as a political power struggle, it has taken on an ethnic dimension and includes evidence of ethnically targeted killings, according to the U.N. mission in South Sudan.
Some observers have said both sides may want to gain the upper hand militarily before beginning to discuss a possible cease-fire.
South Sudan is the world's youngest nation, having seceded from Sudan in 2011 after decades of war.
Journalist Mading Ngor contributed to this report.