. U.S. will act if necessary after southern Sudan attack

. U.S. will act if necessary after southern Sudan attack

The United States will take further action if necessary after U.S. forces attacked in South Sudan , President Barack Obama said Sunday amid growing fears that the country could slide into civil war .

" As I watched the situation in South Sudan , I will take further action to support the security of U.S. citizens , personnel and property , including our embassy in South Sudan , " Obama wrote in a letter to Congress .

Four U.S. soldiers wounded in South Sudan when their planes were shot as they head to Bor town to evacuate U.S. citizens , the Pentagon said Saturday .

Three helicopters were forced to return to Uganda with one aircraft shot and a fuel leak , diplomatic sources said military and Uganda earlier told AFP .

The U.S. said it has now been safely evacuated its citizens from South Sudan rebel-held drill on Sunday , a day after the rescue mission was aborted .

State Department spokeswoman Jen Psaki said in a statement , that the helicopters used in the successful evacuation , and carried along with the UN and the government of South Sudan .

"U.S. citizens and citizens of our partner countries flown from Bor to Juba with the UN and U.S. civilian helicopters , " he said .

"The United States and the United Nations , which has lead to secure the airport Bor in Southern Sudan , to take steps to ensure that fighting factions realized that this flight was a humanitarian mission . "

The announcement came 24 hours after the Pentagon asserted that the three Americans were shot Osprey aircraft when approaching Bor , injuring four U.S. soldiers and air force to headed towards Uganda .

The State Department statement said about 380 U.S. officials and private citizens , plus another 300 citizens have so far been taken to Nairobi and other locations in the four and five charter flights of military aircraft .

" Other U.S. citizens may have left the country through other means . We highly recommend U.S. citizens in South Sudan to get going , " added Psaki .

U.S. deploying 45 troops on Wednesday to protect personnel and assets in the American South Sudan , in the midst of intensive fighting between rebels and government forces .