(Adds Obama's letter)
WASHINGTON, Dec 22 (Reuters) - U.S. citizens were safely evacuated on Sunday from Bor to Juba in South Sudan, the State Department said as fears grew of an all-out ethnic civil war in the landlocked African country.
"This morning, the United States - in coordination with the United Nations and in consultation with the South Sudanese government - safely evacuated American citizens from Bor, South Sudan. U.S. citizens and citizens from our partner nations were flown from Bor to Juba on U.N. and U.S. civilian helicopters," the State Department said in a statement.
It did not specify how many Americans were transported to Juba, a day after three U.S. aircraft came under fire from unidentified forces while attempting an evacuation.
"As I monitor the situation in South Sudan, I may take further action to support the security of U.S. citizens, personnel, and property, including our embassy in South Sudan," President Barack Obama said in a letter to leaders in the U.S. House of Representatives and the Senate.
Overall about 380 U.S. officials and private citizens have been evacuated away from the fighting in South Sudan, the State Department said. It said it also flew about 300 citizens of other countries to Nairobi and other locations outside South Sudan on four chartered flights and five military aircraft.
"The U.S. government is doing everything possible to ensure the safety and security of United States citizens in South Sudan," said the statement by Jen Psaki, the State Department's spokeswoman.
It said the United States and the United Nations had taken steps to ensure fighting factions were aware that the evacuation flights were on a humanitarian mission.
Obama said in his letter to leaders in Congress that "approximately 46 additional U.S. military personnel" were deployed by aircraft on Saturday to evacuate Americans from the conflict. After the aircraft came under fire as they approached Bor on Saturday, the operation was curtailed "due to security considerations," Obama said.
The U.S. military said four of its members were wounded in the attacks.
The United Nations says hundreds of people have been killed in the latest conflict in South Sudan. (Reporting By Susan Cornwell, Ros Krasny; Editing by Doina Chiacu and Christopher Wilson)