It is expected that the six Bulgarian citizens that had been captured by insurgents in Sudan should be released on Thursday or Friday at the latest.

This was announced by Georgi Spasov, the chairman of the board of directors of Heli Air, the airline company of which the captured Bulgarians are employees, in an interview for private NOVA TV station on Thursday.

Spasov said that the airline company had contacted the families of the helicopter's crew members, informing them that the six Bulgarians were in good condition, were well looked after and their release was expected soon.

The helicopter, which was operating under a contract for the United Nations World Food Programme (WFP), was conducting a flight from Rumbek in South Sudan to Khartoum in Sudan.

The crew was captured by members of the Sudan People's Liberation Movement-North (SPLM-North) on Monday, when it did an emergency landing in the city of Kaduqli.

Although the helicopter had permissions to enter the airspace of both Sudan and South Sudan, it went into a zone controlled by the insurgents.

Employees at the operations centre of Heli Air noticed on Monday morning that one of their helicopters remained still.

The initial hypothesis of a crash was dismissed as the signal system was not indicating that such an incident had taken place.

It emerged on Wednesday that the insurgents are not going to demand ransom as they had mistakenly taken the Bulgarian helicopter for an aircraft of the Sudanese government they are fighting against.

Heli Air has an experience of 25 years in conducting such operations and at present it has eight aircraft that participate in humanitarian missions in Africa.

Bulgaria's Foreign Minister Daniel Mitov assured on Wednesday that the Bulgarians were not taken hostage and that the UN was holding high-level negotiations for their release.