The US has said it is disappointed at the failure of South Sudan's leaders to agree to form a power-sharing government.
The Assistant Secretary of State for African Affairs, Tibor Nagy, questioned whether President Salva Kiir and his rival Riek Machar are the right people to lead the peace process.
He said the US was considering all options to put pressure on individuals who would impede peace and promote conflict in the country.
Conflict broke out in South Sudan in 2013, two years after it became an independent nation, after a fallout between President Kiir and his then deputy Mr Machar.
Thousands of people have been killed in the conflict and over two million displaced.
A power-sharing agreement was signed between the warring parties in August 2018 in a bid to bring the five-year civil war to an end.
The deadline to set up a new administration was 12 November, but the two leaders agreed to delay by 100 days the formation of a government of national unity following a meeting in the Ugandan capital, Kampala.
On Wednesday, the UN Security Council said it was concerned that there was no substantive progress on the implementation of key elements of the peace agreement.