The UN Children's Agency (UNICEF) said on Tuesday three of its subcontractors have been detained last week in Pagak area, the headquarters of the opposition group loyal to South Sudan's rebel leader Riek Machar.

Timothy James Irwin, UNICEF's chief communications officer in South Sudan, said in a statement that three South Sudanese working for Montrose, an organization contracted by UNICEF to carry out education surveys in Mathiang fled the area on 7 July along with other humanitarian actors, and were detained in Pagak area upon arrival.

Irwin further said negotiations for the release of the three UNICEF subcontractors who were detained in Pagak are ongoing.

Last week, heavy fighting erupted in the area between government troops and SPLA-IO fighters loyal to Riek Machar near the rebel stronghold despite declaration of a unilateral ceasefire by President Kiir.

Dickson Gatluak, a military spokesman for the SPLA-IO splinter group under the current First Vice President Taban Deng Gai blamed opposition troops allied to former first vice president Riek Machar for abducting the aid workers.

Lam Paul Gabriel, deputy military spokesman of SPLA-IO denied detaining the three aid workers in Pagak.”SPLA IO under the leadership of Dr. Riek Machar Teny does not harass NGOs or UN staffs. These are our partners not enemies. If they are in Pagak, then they are safe with the civilians in the liberated area. The SPLA-IO did not get any formal complaint from UNICEF regarding this baseless accusation,” he said.

Aid workers have been increasingly targeted in various conflict zones in the country, where at least 79 humanitarian workers have been killed since the civil war began in 2013.

In March this year, unknown gunmen killed six aid workers along the Juba-Pibor road.