The UN's 15-member council threatened sanctions "against any party" late Friday in a joint statement aimed apparently at President Salva Kiir, who signed the latest deal last Wednesday, but listed "serious" reservations.

Rebel leader and ex-president Riek Machar signed the deal a week ago.

Late on Thursday, rebels accused the young nation's army of attacking their positions in the northern state of Unity.

A spokesman for Kiir's presidential office, Ateny Wek Ateny said that it was difficult to ascertain which side had started the fighting.

Kiir had ordered troops to "stop shooting and remain in barracks where they are, but they can shoot in self defense once attacked," Ateny added.

Kiir's 16 reservations, listed in a document handed out to diplomats and regional leaders after his signing on Wednesday, includes questions over power-sharing with rebels.

Numerous failed bids

South Sudan has endured seven failed ceasefire bids since December 2013 when Kiir, an ethnic Dinka, accused Machar, an ethnic Nuer, of trying to oust him.

Resulting warfare, marked by ethnic killings, gang rapes and child soldier recruitment, claimed thousands of lives and drove some 2.2 million people from their homes (pictured above). Many sought shelter at UN bases.

The world's newest country broke away from Sudan in 2011.

Arms embargo

The council, in a presidential statement approved by all 15 members late Friday, warned South Sudan's factions that the UN was ready to "consider appropriate measures," including an "arms embargo and additional targeted sanctions."

Those responsible for human rights violations in South Sudan during the crisis must face justice, it said.

The latest ceasefire deal foresees the return of rebel leader Machar to the post of first vice president, a job from which he was sacked in July 2013.

Brokered by regional bloc

The deal, brokered by the regional eight-nation IGAD bloc, along with the UN, the African Union, China, Britain, Norway and the United States, calls for a transitional government to be established within 90 days.

It also foresees humanitarian assistance and institutional reforms.

The UN Security Council said it would support implementation of the agreement by moving swiftly to update the mandate of the region's UN peacekeeping mission.

ipj/lw (AFP, dpa, AP)