South Sudan President Salva Kiir attends an urgent session for the Summit of the Inter-Governmental Authority on Development on South Sudan in Ethiopia's capital, Addis Ababa. Picture: Tiksa Negeri

United Nations - Voicing alarm over the crisis in South Sudan, the UN Security Council threatened Friday to slap sanctions on warring factions for failing to live up to a peace deal signed three months ago.

The warning came in a unanimous statement agreed to ahead of a South Sudan visit by Security Council ambassadors next week during which the envoys are to deliver the message directly to the country's leaders.

“The actions of President Salva Kiir and former vice president Riek Machar in continuing to pursue a military solution to this conflict are unacceptable,” said the 15-member council.

Under a peace deal signed in May, Kiir and Machar are to establish a unity government by August 10, Sunday, but there are no signs they will meet that deadline.

The council “expresses its readiness to consider, in consultations with relevant partners, (...) all appropriate measures, including targeted sanctions against those who take action that undermines the peace, stability and security of South Sudan, including those who prevent the implementation of these agreements,” the statement said.

A new round of peace talks opened in Ethiopia on Monday even as fighting raged on the ground, but there has been little reported progress.

International alarm is growing over a looming famine in South Sudan, which the United Nations has described as the world's worst food crisis affecting at least 3.9 million people, or one in three.

Thousands have been killed and over 1.5 million have fled more than seven months of fighting between government troops, mutinous soldiers and ragtag militia forces divided by tribe.