Juba — Four United States military personnel were injured on Saturday when their aircraft was "shot at" in the rebel-held Jonglei state capital, Bor.
The US embassy in Juba confirmed the incident, which comes a week after violence broke out in country's capital, later spreading to other states.
"The #Bor evac flight came under fire, preventing the evacuation attempt. Four U.S. Service members were injured during the attack", the US embassy tweeted.
So far the US Embassy has evacuated 450 American citizens and other foreign nationals from the capital Juba, but was has so far been unable to begin evacuations from Bor, the capital of Jonglei.
Army defectors took control of Bor earlier this week but the spokesperson for the South Sudanese army (SPLA) said on Saturday that they had regained control of the town, which is just 200km north of the capital.
More than 500 people, the United Nations said, have since been killed since Sunday with an estimated 35,000 reportedly displaced in the worst ever conflict in the country's post-secession era.
South Sudan president Salva Kiir has blamed his former deputy Riek Machar and other opponents within the ruling SPLM of instigating the incident, which initially involved the presidential guards. Machar, however, denied any involvement saying it was a move to silence those opposed to Kiir's leadership.
The US president Barrack Obama said the new nation risks returning to full scale war, if the volatile situation was not controlled. The Obama administration also dispatched Donald Booth, its special envoy to the two Sudans for talks on the matter.
UGANDAN ARMY DENIES BOMBING BOR
Meanwhile, the Ugandan army has strongly refuted earlier reports that its military aircraft bombarded rebel-held positions in Bor on Saturday.
"No Ugandan planes are in Bor nor are there any Ugandan planes that have been shot," Lt. Col. Paddy Ankunda, the spokesman, of the Uganda People's Defence Forces (UPDF) said in an email to Sudan Tribune.
Gen. Katumba Wamala, the army chief of staff also denied his army's alleged involvement in the conflict, which threatens peace and stability in South Sudan.
"Bor is a couple of miles from Juba, unless we posses supernatural powers, we couldn't have moved that fast", he tweeted in response to a journalist.
The Ugandan army on Thursday said it had deployed troops in South Sudan to help secure its citizens from the increasingly volatile country.
More than 150 Ugandans, according to media reports, were evacuated from Juba by a military aircraft that had flown in Ugandan special forces to the South Sudan capital.
Uganda has a long history of security cooperation with South Sudan, dating back to the long struggle for independence from Sudan and, more recenyly, in operations against the Lord's Resistance Army rebel group, which originated in northern Uganda.