The White House chastised President Salva Kiir of South Sudan for refusing to sign a peace agreement to halt that nation’s civil war, The New York Times reported Wednesday.

The US threatened to pursue sanctions against “those who undermine the peace process.” Susan E. Rice, the national security adviser, said in a statement that “there must be consequences for those who continue to stand in the way of peace.”

She added that the United States had begun consultations at the United Nations and with regional partners to initiate action in the Security Council.

This summer, US President Barack Obama met with the region’s leaders during a trip to Africa and urged them to seek an end to the fighting. The leaders agreed to seek sanctions if the warring parties refused to sign a peace deal by Monday. At the deadline, Kiir declined to sign, saying in a Twitter message: “If it is signed today and then tomorrow we go back to war, then what have we achieved?”

On the government's Twitter account Monday, Kiir said, "Peace that cannot be sustained cannot be signed."

South Sudan's civil war erupted in December 2013 following a political dispute between President Kiir and Machar, his former deputy.