Washington, April 4 (IANS): US President Barack Obama Thursday authorised sanctions against those in South Sudan whose actions threaten the peace, security or stability of the country born about three years ago.

Obama signed an executive order declaring that the situation in South Sudan "poses an unusual and extraordinary threat to the national security and foreign policy of the United States," Xinhua reported.

He declared "a national emergency" to deal with the threat, authorising his secretaries of treasury and state to freeze the assets of those who threaten the peace, stability or security of South Sudan, commit human rights abuses or undermine transition or institutions in the country.

White House spokesperson Jay Carney noted that thousands have been killed since clashes broke out in December between forces loyal to South Sudan's President Salva Kiir and Riek Machar, the country's former deputy president and rebel leader now.

Despite a ceasefire agreement reached in January, "the cycle of violence and conflict continues," Carney said in a statement.

"Both the government of South Sudan and Riek Machar's rebels must immediately engage in and follow through on the inclusive peace process led by the Intergovernmental Authority on Development and resolve this conflict," Carney said.

"They must end military actions and hold accountable those responsible for violence against civilians," he added. "There is no room for excuses or delay."