South Sudan

A United Nations helicopter transporting wounded civilians from Bor, the capital of South Sudan's Jonglei state, arrives at the airport in Juba, South Sudan, on Sunday. (United Nations Mission in South Sudan / December 22, 2013)

HONOLULU -- President Obama told congressional leaders Sunday that he was closely monitoring the unrest in South Sudan, after four U.S. service members were attacked near Bor, and said he “may take further action to support the security of U.S. citizens, personnel and property, including our Embassy, in South Sudan.”

After an aborted rescue mission of U.S. citizens Saturday, 380 U.S. officials and private citizens -- as well as 300 citizens of other nations -- were evacuated from South Sudan on chartered flights and military aircraft, according to a statement Sunday from State Department spokeswoman Jen Psaki.

Officials “took steps to ensure fighting factions were aware these flights were a humanitarian mission,” she said. “We strongly recommend U.S. citizens in South Sudan depart immediately, and we encourage those who remain to keep in touch with the Embassy and update their locations and status by contacting us at SouthSudanEmergencyUSC@state.gov,” Psaki said.

The president’s Sunday missive notifying leaders of the House and Senate that U.S. forces are engaged abroad was standard operating procedure. White House officials said the notification should not be interpreted as an escalation of U.S. military operations in the region.

But Obama, who has just begun a two-week vacation with his family in Hawaii, appeared to be leaving his options open as he receives daily briefings from his national security advisors on the developing situation in South Sudan.

The four servicemen were wounded Saturday when South Sudanese militias fired on three U.S. military aircraft that were en route to Bor, the capital of Jonglei state, where South Sudan’s army has been engaged in a struggle over control of the town with a rebel military faction aligned with former Vice President Riek Machar.

In new details revealed in Obama’s letter to the House speaker and leader of the U.S. Senate, the president said about 45 additional U.S. military personnel were deployed Saturday on the mission to evacuate U.S. citizens from Bor. The rescue mission was aborted after the militia fired on U.S. planes.

Four U.S. service members were injured by gunfire, according to a statement from the U.S. military's African command. Obama was told Saturday that all were in stable condition. The service members were treated in Nairobi, Kenya, after their aircraft was diverted to Kampala, the Ugandan capital, according to the Associated Press.

The U.S. embassy in Juba, the capital of South Sudan, tweeted Sunday that “there is still a lot of work to be done” and asked those with information about American citizens seeking evacuation to contact the embassy. It was unclear when the next evacuation flight would be.

As the army has lost control of key regions in South Sudan, the fledgling nation has spiraled toward civil war with the military divided and defectors taking control of key areas. The crisis has been fueled by the clash between President Salva Kiir and Machar, the former vice president whom Kiir dismissed in July.

Kiir has accused Machar of attempting a coup. The former vice president denied the allegation, but there are reports that rebel factions in Jonglei and Unity states are under his command.

Obama received a second briefing on the situation in South Sudan on Saturday after National Security Advisor Susan Rice held a meeting with senior members of the national security team, as well as U.S. personnel in Juba and the region.

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maeve.reston@latimes.com