WASHINGTON, Dec. 21 -- U.S. President Barack Obama on Saturday urged factions in South Sudan to resolve conflict through peaceful negotiations, warning the use of force to seize power would lead to the end of support from the U.S. and international community.

Obama, who is vacationing in Hawaii, was briefed on Air Force One Friday night on the status of four American soldiers who were wounded during an evacuation operation in South Sudan, the White House said in a statement.

The president on Saturday morning participated in a secure call with National Security Advisor Susan Rice and other top aides in his national security team, who briefed him on the situation in South Sudan as well as the safety of American citizens in Bor and the U.S. Embassy personnel in Juba, capital of South Sudan.

The U.S. African Command confirmed that four American service members were injured Saturday when their aircraft came under ground fire in South Sudan during a mission to evacuate American citizens in Bor. The mission was aborted as the aircraft diverted to an airfield in the neighboring Uganda.

Obama reaffirmed the importance of continuing to work with the United Nations to secure American citizens in Bor, while underscoring that South Sudan's leaders have "a responsibility to support our efforts to secure American personnel and citizens in Juba and Bor," the White House said.

Obama also underscored the urgency of helping to support efforts to resolve the differences within South Sudan through dialogue, adding that continued violence will endanger the people of South Sudan and the hard-earned progress of independence.

"This conflict can only be resolved peacefully through negotiations. Any effort to seize power through the use of military force will result in the end of longstanding support from the United States and the international community," the statement said.

As violence has been escalating in South Sudan, U.S. Secretary of State John Kerry on Friday sent Special Envoy for Sudan and South Sudan Donald Booth to the region to "support regional efforts already underway" to end the armed conflict in South Sudan.

Kerry called South Sudanese President Salva Kiir Thursday night and told him to protect all civilians and work toward reconciliation. He demanded for an immediate end to the violence and intensified dialogue to resolve the conflict by different ethnic and political groups in the young African country.

On Wednesday, Obama deployed 45 U.S. troops to the African country to protect its citizens and property. The U.S. government on Thursday evacuated more citizens from South Sudan, as a private charter flight lifted some 130 persons from Juba.

Fighting broke out last Sunday between forces loyal to President Kiir and his former deputy Riek Machar, who was removed from office in July. Kiir accused Machar of being behind what he called an attempted coup. The fighting has triggered off a humanitarian crisis, forcing foreigners to flee the country and some 20,000 civilians to seek refuge at the UN Compound in Juba.