The revelation has sparked outrage among experts and campaigners who say it undermines a crucial element of the peace deal that was signed last year, following five years of a brutal civil war that has killed at least 400,000 and displaced millions.

The two-year contract pays $3.7m (£2.8m) to a California-based lobby group called Gainful Solutions, which agrees, among other aims, to "delay and ultimately block establishment of the hybrid court":

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Gainful Solutions is run by Michael Ranneberger, a former US ambassador to Kenya and Mali.

The contract between the two parties was published in the Foreign Agents Registration Act section of the Justice Department website, Reuters news agency explains, as the act requires lobbyists acting on behalf of foreign agents in the United States to register the relationship.

South Sudan’s Deputy Chief of Mission in the United States Gordon Buay has denied his government has any intention of abolishing the hybrid court, telling AP news agency the priority was for reconciliation rather than punitive justice.