The UN Security Council on Wednesday unanimously passed a resolution giving Sudan and South Sudan 48 hours to halt hostilities or face potential sanctions.

With China and Russia joining the growing calls for a halt to the growing border conflict, the 15-member council gave emphatic backing to African Union efforts to halt violence and get peace negotiations started.

Russia and China had opposed talk of sanctions during negotiations on the US-drafted resolution which calls on the neighbors to "immediately cease all hostilities" and withdraw troops to their own territory.

Resolution 2046 says they must give a written commitment to halt fighting within 48 hours to the African Union and the Security Council.

The council ordered the two sides to start peace talks within two weeks under the auspices of African Union mediators.

The resolution threatens "additional measures" under Article 41 of the UN Charter -- which allows for non-military sanctions -- if either side fails.

"The current conflict between Sudan and South Sudan is on the verge of becoming a full scale and sustained war," US ambassador Susan Rice told the council.

"Both countries are on the brink of returning to the horrors of the past and threaten to take the entire region with them," she added, referring to the civil war between the two sides before their formal separation last year.

More than two million people died in the two-decade conflict up to 2005.

Tensions have quickly risen since their split in July -- with no border agreed nor an accord on how to share revenue from oil reserves which straddle the two sides.

Rice said the resolution sets "tight deadlines for concrete action."

"In the history of this conflict there is a long litany of promises made and promises broken. So as this resolution indicates we will judge the parties by their actions not simply their words."

China, which has strong trade ties to both countries and is a key customer for Sudanese oil, had strongly opposed the threat of sanctions in the resolution but eventually decided to back it.

Diplomats said the African Union's strong call for potential sanctions had forced China's hand. China normally backs efforts by regional groups to settle conflicts and could not be seen going against the AU, they added.

China "has been deeply worried about the recent deterioration of relations between the two countries," said its UN envoy Li Baodong. He called on them both to "stick to the path of peace."

Li reaffirmed China's doubts about sanctions, saying that the international community must not impose "unbalanced pressure" on the two countries.

"We are always very cautious about the use or threat of sanctions," while adding that China voted for the resolution "taking into account" the African Union's action.

South Africa, one of two African members of the council, also raised fears over the "escalation" between Sudan and South Sudan.

"It is clear that there can be no military solution to resolving the outstanding issues," said South Africa's UN envoy Baso Sangqu.

He said the resolution would bolster the AU effort to get the two sides away from "the logic of war".