A US Air Force cargo planes and military personnel were at the Juba International Airport ready to rescue evacuees from South Sudan on December 21, 2013.
Four US troops were wounded in South Sudan when their aircraft were hit by small arms fire Saturday during a mission to evacuate Americans, the Pentagon said in a statement.
Three Osprey hybrid aircraft -- which can take off vertically like a helicopter but resemble a normal plane and are designed for longer-range tasks -- had been headed for the rebel-held city of Bor, but had to divert to Uganda.
US and Ugandan officials initially said one of the Ospreys was hit and leaking fuel after the attack, but the Pentagon statement later confirmed all three aircraft had sustained damage.
"The damaged aircraft diverted to Entebbe, Uganda, where the wounded were transferred onboard a US Air Force C-17 and flown to Nairobi, Kenya for medical treatment," an updated Pentagon statement said.
"All four service members were treated and are in stable condition."
The United States deployed 45 troops on Wednesday to protect American personnel and assets in South Sudan, amid intensifying fighting between rebels and government forces.
In a letter to Congress, President Barack Obama said the force "will remain in South Sudan until the security situation becomes such that it is no longer needed."
"Although equipped for combat, this force was deployed for the purpose of protecting US citizens and property," he added.
Violence erupted after a meeting last week of leaders of the ruling Sudan People's Liberation Movement (SPLM) failed to ease tensions in the party.
South Sudan President Salva Kiir has accused Machar, whom he fired in July along with his entire cabinet, of staging an attempted coup. The former vice president has denied the charge, but his whereabouts are unknown.
Even as diplomatic initiatives were multiplying in South Sudan, the death toll continued to climb as violence spread between rival ethnic groups.
Six days into the battles between followers of Kiir, an ethnic Dinka, and Machar, a Nuer, at least 500 people have been killed in Juba alone.
Foreign governments meanwhile scrambled to get their nationals out of harm's way.