WASHINGTON  - Elections set to be held in South Sudan in December are not on a path for a credible process without urgent action, a senior U.S. State Department official warned on Friday, as the government lags in its preparations.

The official, asked in an interview with Reuters whether the election was on the path to be a sham process, said yes, barring any urgent action.

South Sudan is planning national elections later this year to choose leaders to succeed the current transitional government, which includes President Salva Kiir and First Vice President Riek Machar, whose respective forces battled each other during the 2013-2018 civil war.

In 2022, Kiir said the transitional government would remain in power for another two years, delaying scheduled elections.

On the likelihood the elections proceed in December as planned, the U.S. official said: "I give it 50/50."

The official, speaking on condition of anonymity, warned that the U.S. would look to options including sanctions and adjusting its diplomatic platform in the country if elections were to be delayed or violence breaks out.

"If there's either a delay or violence, I think we would look at the whole suite of options, including sanctions," the official said.

Other options could include looking at Washington's development assistance and other forms of engagement, the official said.

A spokesperson for the government of South Sudan did not immediately reply to a request for comment.

Deputy Assistant Secretary for East Africa, Sudan and South Sudan Peter Lord traveled to the country last week, during which he called on South Sudan's leaders to take steps required to hold credible and peaceful elections in December, according to the embassy.

South Sudan has been formally at peace since a 2018 deal that ended a five-year conflict responsible for hundreds of thousands of deaths, but localized violence between rival communities flares frequently.

But the U.S. official on Friday warned that South Sudan had not followed through on commitments from two years ago, including doing a census, drafting a constitution and setting up all necessary democratic institutions for the elections to take place.

The official added that electoral institutions were just established and there has not been a thorough or considered process.

The senior official believes that Kiir wants the elections to take place for the legitimacy they would provide, but said that there are those around him - including Machar - who do not want them as they risk losing in a political contest.

Machar and others have taken a position that everything committed to in the extended peace agreement needs to be completed, the official said, adding it could not all be done in time for the elections.

Kiir and others are using Machar's position - as well as other obstructionist actions he has taken, such as not providing a list of names for unified forces - as an excuse for not taking additional action, the official said.

Civil society in South Sudan also recognizes that not enough has been done, the official added.

"There is a lot of concern that there will be bad violence. So there's a high appetite for elections, but they also know that the ... government hasn't done what it needs to do."

(Reporting by Daphne Psaledakis; Editing by Don Durfee and Jonathan Oatis)