File Photo: Billboard with South Sudan President Salva Kiir Mayardit advertising the National Dialogue process, Wau. AFP
"This announcement demonstrates the persistent and collective failure of South Sudan's leaders to create the conditions necessary to hold credible and peaceful elections," said a joint statement from the three governments.
South Sudan won independence from Sudan in 2011 but was plunged into a civil war two years later that killed an estimated 400,000 people.
A 2018 peace deal brought together President Salva Kiir and bitter rival Vice President Riek Machar. However, efforts to write a constitution and hold the country's first-ever elections have been repeatedly delayed.
Last week, Kiir's office announced that voting planned for December would be pushed back by another two years, ahead of a Sunday deadline for the transitional government to be dissolved.
Cabinet Affairs Minister Martin Elia Lomuro said the extension was "in response to the recommendations from both electoral institutions and the security sector."
The three countries "acknowledged" that polls could not be held as scheduled in December, and blamed "a lack of political will."
"Responsibility for this failure is shared by all parties in the transitional government," said the statement. "As South Sudan's leaders vie for power and fail to organize credible and peaceful elections, the people of South Sudan suffer the consequences."
Earlier this week, the United Nations expressed "regret and disappointment" at the delay.
"Two years ago, we were in a similar situation as we are today and gave our support specifically under the condition that there would be no more extensions," said UN special representative Nicholas Haysom in a statement.
South Sudan has battled flooding, hunger and violence, while its leaders have appeared reluctant to risk going to the polls and are accused of massive corruption.
Earlier this month, the UN's humanitarian agency warned that more than 700,000 people had been impacted by flooding, with aid failing to meet many in need.
South Sudan boasts plentiful oil resources, but the vital source of revenue was cut in February when an export pipeline was damaged in war-torn Sudan.
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