UNITED NATIONS, Jan. 23-- UN Secretary-General Ban Ki- moon on Friday welcomed a peace agreement among South Sudan's rival factions, calling for immediate implementation of the pact.

"The Secretary-General reminds the parties that time is running out," said UN spokesperson Stephane Dujarric while reading a statement issued here.

He urged them to use the opportunity of the forthcoming Intergovernmental Authority on Development Summit to reach a final agreement on ending the conflict, including a power-sharing formula and measures to address its root causes and ensure accountability, Dujarric said.

South Sudan's rival factions of the ruling Sudan People's Liberation Movement (SPLM) on Wednesday signed an agreement in Arusha, Tanzania, after fighting for power for the past year.

The agreement commits the SPLM to rebuilding and democratizing the movement internally in order to promote national harmony and end the conflict afflicting the people of South Sudan.

In Friday's statement, Ban called for the immediate implementation of the Arusha Agreement, "particularly the recommitment of President Salva Kiir and Dr. Riek Machar to respect the cessation of hostilities agreement," and encouraged the signatories to resolve the leadership issues of the SPLM.

Fighting broke out in South Sudan, the world's youngest country, in December 2013 when Kiir accused his sacked deputy Machar of attempting a coup.

The conflict has killed tens of thousands of people, driving 1. 5 million South Sudanese from their homes and leaving almost 5 million in dire need of humanitarian assistance.