The United Nations (UN) Security Council has adopted a resolution that threatens an arms embargo on South Sudan and sanctions against six people if fighting doesn't stop by June 30.

The US-sponsored resolution passed on Thursday would renew existing sanctions against South Sudanese officials until July 15.

It asked Secretary-General Antonio Guterres to report by June 30 on whether fighting is taking place and whether "a viable political agreement" has been reached.

The resolution said in the absence of a cessation of hostilities by June 30, the council would consider freezing the assets and banning travel for six officials, including Defence Minister Kuol Manyang Juuk, former army chief Paul Malong, Minister of Information Michael Lueth, and deputy chief of defence for logistics in the South Sudan Army Malek Reuben Riak Rengu.

The resolution, approved by a 9-0 vote with six abstentions, was a watered-down version of a draft measure proposed by the United States, whose ambassador, Nikki Haley, wrote in The Washington Post on Wednesday that the administration had "lost patience with the status quo" in South Sudan.

"What we need now is concrete action by the full international community to hold these warring parties accountable," Haley said in impassioned remarks before the vote.

She called the resolution a "modest step" that would extend sanctions for 45 days and demand a cessation of hostilities.

'Tragic development'

Among the countries abstaining was Ethiopia, which was critical of the resolution's timing with a peace process mediated by the Intergovernmental Authority on Development (IGAD) still ongoing.

"The adoption of the draft resolution tabled before us will be detrimental to the process. It is a very, very tragic development indeed," Ethiopia's Ambassador Tekedda Alemu said.

On May 23, a round of talks organised by IGAD in Ethiopia's capital Addis Ababa ended without agreement.

A ruinous civil war erupted in South Sudan in December 2013, two years after independence from Sudan, when forces loyal to President Salva Kiir started fighting those allied to his former deputy, Riek Machar.

Tens of thousands of people have been killed in the war, while nearly a third of the country's 12-million people were forced from their homes.

A ceasefire signed last December broke down within hours.