The African Union has demanded sanctions and an arms embargo be imposed on South Sudan's warring leaders to stem an escalation in the country's 17-month-old civil conflict.

"The people of South Sudan have already been devastated by war," said a statement from the AU's Peace and Security Council late Saturday, warning "the current escalation threatens to unleash irreversible consequences for this young nation".

President Salva Kiir and his arch-rival, rebel chief Riek Machar, have come in for fierce international criticism for failing to end a civil war that has been seen accusations of gross human rights abuses.

The UN Security Council has repeatedly threatened sanctions.

Warning of "untold suffering inflicted on the civilian population in total disregard of international humanitarian law," the AU called on the Security Council's Sanctions Committee "to designate individuals and entities" as well as for the "immediate imposition of an arms embargo."
The 54-member AU's council also expressed "deep disappointment over the failure of the leaders of the belligerent parties in South Sudan to rise above personal and factional political interests."

South Sudan's government launched a major assault against rebels in late April in one of its heaviest offensives yet, cutting off over 650,000 people from aid, with gunmen raping, torching towns and looting relief supplies, according to the United Nations and aid agencies.

The rebels retaliated with a major counter-attack, including an assault on Malakal, the state capital of Upper Nile and the gateway to the country's last remaining major oil fields.

Thy government claims to be in full control of Upper Nile's oil fields, although rebels have rejected the claim.

Kiir has called proposed international sanctions "unproductive" and warned they would only "fan the flames" of war.
Washington's envoy to the UN, Samantha Power, this week said the US was working with the UN to gather evidence for possible sanctions, condemning Kiir and Machar for their "shameful disregard for the devastating humanitarian crisis."

The European Union and United States placed asset freezes and travel bans last year on commanders from both sides, but the sanctions have made little if any impact on the worsening war.

Over half of the country's 12 million people are in need of aid, with 2.5 million people facing severe food insecurity, according to the UN.