JUBA- President Barack Obama Sunday firmly vowed to take more action in South Sudan if needed amid growing fighting after deploying extra US troops, as the United Nations promised to send more peacekeepers.
The announcements came as world leaders embarked on a diplomatic push to pull the world's youngest nation back from the brink of all-out civil war.
Special envoys from the United States and Nigeria were expected in the capital Juba following a mission by foreign ministers from east Africa and the Horn.
Obama revealed that US troops attacked by unidentified gunmen Saturday as they approached the rebel-held city of Bor aboard CV-22 Osprey tiltrotor aircraft were part of a unit of about 46 troops sent that day to help evacuate Americans.
That contingent was in addition to another 45 troops sent this week to help protect US citizens, personnel and property at Washington's embassy in the capital Juba.
"As I monitor the situation in South Sudan, I may take further action to support the security of US citizens, personnel and property, including our embassy, in South Sudan," Obama wrote in a letter to Congress.
Foreign governments, including in Britain, Kenya, Lebanon, Uganda and the US, have been evacuating their nationals.
The United States earlier safely evacuated US nationals from Bor, a day after the aborted mission in which four US servicemen were wounded.
Obama has called for an end to the violence, warning the country was on the "precipice" of civil war and that any military coup would trigger an end to diplomatic and economic support from Washington and its allies.