There have been a number of false dawns when it comes to elections in South Sudan, but the authorities have said the long-delayed first-ever vote will take place in December.

The leaders of the world's youngest country have not been tested at the ballot box since independence in 2011 and President Salva Kiir has been in office for 15 years.

According to the original plan, the general election was supposed to have happened in 2015 but a civil war meant that had to be postponed.

The 2018 peace deal, which created a unity government with Kiir at its helm and rival Riek Machar as his deputy, envisioned an election in 2022 but the vote was never organised amid tension between the country's leaders.

Continued issues between the two men could yet delay the vote further.

Machar was sacked as vice-president and arrested earlier last year and charged with murder, treason and crimes against humanity, which he denies. He has been under house arrest in the capital, Juba, since March last year as fighting persists in some areas of the country.

There have been warnings, including form the UN, that the violence could once again spill over into full-scale civil war.

When announcing the 22 December date for the vote, electoral chief Abednego Akok Kacuol acknowledged that unresolved legal amendments and persistent funding gaps continued to hamper poll preparations.

"The political will is not ours; it lies with the government," he said.

Asked what would happen if funds were not secured within six months, Kacuol said his commission would continue planning while adjusting toward a "realistic electoral timeline".

In a statement on Monday, the presidency said Kiir was committed to implementing the 2018 peace agreement and keeping South Sudan on track toward peaceful, democratic elections.

It said preparations for inter-party dialogue on election-related issues were progressing and would provide a platform for building consensus among political stakeholders.

But opposition groups and civil society organisations have raised concerns over security conditions, political freedoms and electoral readiness. 

The Sudan People's Liberation Movement in Opposition (SPLM-IO), the party of Machar, warned about the poll preparations, saying holding elections remained a "dangerous" matter.

"Anyone coming to register voters and campaign in territories controlled by the mighty SPLM-IO, you will be a prisoner of war," Nathaniel Pierino, acting chairperson of the group, said in a post on Facebook. 

"Be reminded, the country is at war," he added.