NEW : Bor is where Machar 's forces fired on three U.S. military aircraft that were on an evacuation mission Saturday . U.N. officials hope to have reinforcements in South Sudan by Saturday . The talks ` ` very constructive , '' South Sudan 's foreign minister said . Fighting between rival ethnic groups has resulted in mass killings . Four U.S. Navy sailors were wounded by gunfire on Saturday .
NEW : U.N. officials hope to have reinforcements in South Sudan by Saturday . The talks ` ` very constructive , '' South Sudan 's foreign minister said . Fighting between rival ethnic groups has resulted in mass killings . Four U.S. Navy sailors were wounded by gunfire on Saturday .