It's not yet clear whether the US will impose the sanctions while Kerry is in South Sudan — which, he said recently, he planned to visit during a week of stops that also include Ethiopia, the Democratic Republic of Congo and Angola.
US officials are still trying to persuade three of South Sudan's immediate neighbours to issue similar penalties against people on both sides of the brutal fighting.
A senior state department official travelling with Kerry said the US was still compiling its own list of individuals whose assets could be frozen and who could be banned from travel to the US. The official was not authorised to be identified by name while briefing reporters and spoke on condition of anonymity.
Kerry arrives in the Ethiopian capital of Addis Ababa on Wednesday. While there, he will meet with African Union leaders to discuss a range of security issues confronting the sub-Saharan region, including South Sudan.
The US wants the AU to deploy peacekeeping forces to South Sudan, but that was still being negotiated, the state department official said.
South Sudan has been rocked by violence since December, when President Salva Kiir accused former Vice President Riek Machar of staging a coup. The violence is taking on an increasingly ethnic dimension between Kiir's Dinka community and Machar's Nuer community.
The State Department has not provided additional details of Kerry's visit to South Sudan and usually does not disclose travels to high-threat conflict zones ahead of time for security reasons.
The trip gives Kerry a chance to help shepherd peace in a new area of the world after his nine-month quest to end decades-long tensions between Israel and Palestinian authorities fell flat. Kerry had hoped to at least put the Mideast on a path to peace, but a 29 April deadline to keep talks going passed this week with both sides as far apart as ever.
US sanctions have had slightly better, if mixed, success when deployed in recent days. Kerry and the rest of the Obama administration have imposed several rounds of economic sanctions and travel bans against dozens of Russian and former Ukrainian officials and businesses to punish Moscow, in the White House's view, for inciting unrest against the new pro-Western government in Kiev.
US officials have described the sanctions as pinching Russia, but so far they have not deterred President Vladimir Putin, who has amassed 40 000 troops on his border with Ukraine in what many fear is the first step to an invasion.
Potential of tensions
It's unclear how effective US sanctions would be in South Sudan without similar penalties imposed by Ethiopia, Uganda and Kenya.
Describing the fighting as an extension of a personal battle between Kiir and Machar, the State Department official said the US was well aware of the potential of tensions when the country broke off from Sudan after a 2011 referendum. But, the official said, few expected any fighting to happen so quickly or be so brutal.
The UN Security Council last week expressed "horror" at the recent massacre of several hundred civilians in the city of Bentiu by rebel fighters. It said council members may be willing to impose sanctions if attacks on civilians continue.
In a statement on Tuesday, the UN Secretary-General Ban Ki-Moon called Kiir and demanded assurances that militants who attacked the UN compound in the southern city of Bor and others behind the killings in Bentiu would be apprehended.
He also "called for an immediate halt to the vicious fighting and the appalling killing of South Sudanese civilians" and denounced the attack in Bor as "completely unacceptable".
Kerry was expected to return to Washington on 5 May.
South Sudan army (SPLA) soldiers. (Samir Bol, AFP)