WASHINGTON - The White House said on Wednesday the United States had sent additional US military personnel to South Sudan to boost security of the US embassy in the country.

"The first of these additional personnel, approximately 47 individuals, arrived in South Sudan on July 12, 2016, supported by military aircraft," said US President Barack Obama in a letter to the US House Speaker Paul Ryan.

According to the letter, though equipped for combat, these additional military personnel's main mission would be to protect US citizens and property amid the deteriorating security situation in South Sudan.

"Additional US Army Forces, including approximately 130 military personnel currently pre-positioned in Djibouti, are prepared to provide support," the letter added.

South Sudan descended into civil war in December 2013 following a falling out between President Salva Kiir and his then sacked deputy Riek Machar.

Under a peace deal signed by the two under UN pressure last August, a unity government was formed in April with Machar returning to his old post.

However, tension again rose in past weeks between government troops of Kiir and forces loyal to Machar, raising concerns that the war-torn country could again descend into war.