Resolution 2428 won nine votes in favour, the minimum requirement for adoption. The remaining six members of the Security.Council -- Bolivia, China, Equatorial.Guinea, Ethiopia, Kazakhstan and Russia -- abstained.
Resolution 2428 renews a travel ban and asset freeze against designated individuals and entities until 31 May next year. It also renews the mandate of the Panel of Experts, who assist the work of the sanctions committee, until 1 July 2019.
The resolution adds two individuals to the blacklist for travel ban and asset freeze. They are Malek Reuben Riak Rengu, a former deputy chief of staff of South Sudan's army, and Paul Malong Awan, the former chief of staff of South Sudan's army, who rebelled last year.
The resolution expresses deep concern at the failures of South Sudanese leaders to bring an end to the hostilities and condemns the continued and flagrant violations of previous peace agreements.
The Security.Council adopted a US-drafted resolution on 31 May to renew South Sudan sanctions temporarily till 15 July 2018, to allow time for the introduction of an arms embargo, unless the parties stop fighting and agree on a viable political agreement.
Before the vote, Ethiopian Ambassador to the United Nations Tekeda Alemu, whose country is leading regional efforts to revitalise the South Sudan peace process, told the Security.Council that the timing for the introduction of an arms embargo is not right and asked members not to vote for the US draft.
"That is why we find it difficult to vote in favour of this draft resolution, and why, in our view, other council members should not as well."
US Ambassador to the United Nations Nikki Haley, who spoke before the Ethiopian ambassador, was trying to push the draft through, arguing that the arms embargo is a measure to protect civilians and help stop the violence.
"Peace in South Sudan will not come by letting the parties get their hands on more weapons. The opposite is true. Supporting an arms embargo will show the parties that we are fed up with the delays and the stalling (in the peace process). It will show our resolve to make life better for the people of South Sudan.
"We can come together to show South Sudan that the era of impunity is over. We can show the world that the Security.Council will live up to its responsibility to help maintain international peace and security. Above all, we can send a small signal of hope to the people of South Sudan."
Shortly after its independence from Sudan in 2011, South Sudan plunged into civil war. Up to 300 000 people are estimated to have been killed since late 2013. More than 1.5 million people have fled to neighbouring countries, and many more are internally displaced. The UN sanctions have been in place since 2015.