A South Sudan opposition politician, Peter Mayen Majongdit, has been missing since last week.
It is said unidentified security agents took him away from his residence in Juba.
Majongdit is the head of the People’s Liberal Party, which was established about two months ago.
He hails from Warrap State in the Bahr al Ghazal region.
Mijok Lang Mijak, the party’s top youth leader, told Radio Tamazuj that Majongdit was arrested soon after publication of an article in Juba Monitor in which he criticized the government for borrowing huge amounts of money from Qatar.
He was taken from his home on 1 April at about 11:00 p.m.
Since then the government has brought no charges against him nor notified the party of his whereabouts.
Mijak said in a case of kidnapping or disappearance, it becomes hard for layers to intervene hence calling for the immediate release of Majongdit.
Mijok described the PLP as a new party whose members nonetheless had contributed to the liberation of South Sudan.
Meanwhile in Upper Nile State, three people working for the UN World Food Programme (WFP) have been missing.
George Fominyen, spokesman for WFP in Juba, said that the three workers departed from Malakal in a WFP convoy in the early morning hours of 1 April.
They travelled northward toward Melut to distribute food there.
Fighting broke out on that day in Lul and Akoka along the route that the convoy was traveling.
“Communication with the convoy, which had three persons, was lost. We have not been able to reach our colleagues since then,” said Fominyen.
He disclosed that the three aid workers are all South Sudanese nationality and they are drivers.
The WFP spokesman told Radio Tamazuj that the aid organization is “deeply concerned about their safety and security” and is working tirelessly to ensure that the missing workers are found.
UN Office for Coordination of Humanitarian affairs meanwhile also reported that in another recent incident two other aid workers and 15 drivers of contracted commercial trucks transporting 130 metric tonnes of food supplies to Rom were detained at Khor-Adar for hours.
“They were later released but one truck driver was commandeered to Akoka,” reads an OCHA report.