South Sudanese opposition parties protested Monday at an "exorbitant" $50,000 fee to register ahead of the fragile country's first ever elections, branding it a slap in the face for democracy.

The world's youngest nation is due to go to the polls by the end of the year under a 2018 peace deal, although the United Nations and others say key obstacles still need to be overcome if they are to take place.

Last week, the Political Parties Council, a body set up to prepare for the planned December elections, said political parties had to pay $50,000 or the equivalent in South Sudanese pounds in order to register.

Previously the fee was 20,000 pounds (around $150), but the council has not given a reason for the vast increase.

Dozens of members of a coalition of 14 opposition parties joined a march to the council's headquarters in Juba to deliver a petition protesting at the cost.

"We believe that this exorbitant fee has no basis and is in direct contradiction to the principle of democracy and fair political participation," said Gai Chol Paul, the head of the People's United Front, which was launched in the middle of last year.

"This steep fee only serves to hinder and discourage citizens from exercising their right to participate in the upcoming elections," he said as he handed over the statement to the council.

Since becoming independent from Sudan in July 2011, South Sudan has struggled to find its footing, battling violence, endemic poverty and natural disasters.

Shortly after independence, the country plunged into a devastating 2013-2018 civil war between forces loyal to President Salva Kiir and his sworn enemy Riek Machar that left nearly 400,000 people dead and millions displaced.

A 2018 peace agreement led to a unity government, with Machar serving as vice president to Kiir, but many provisions of the deal remain unfulfilled because of persistent disputes between the rivals.

Machar's party has threatened to boycott the elections unless key tenets of the deal are implemented.

"We are not against the elections. We just feel that a rushed election will not bring any meaningful stability," Machar said in a post on X on Saturday.

"There are too many issues in the peace agreement that must be implemented."

Kiir met the UN's South Sudan envoy Nicholas Haysom last week to discuss the polls, the government said on X.

During the meeting "Kiir emphasised the significance of elections in determining the future of South Sudan and underlined the need for all stakeholders to cooperate in ensuring a smooth and transparent electoral process," it said on Friday.