A spokeswoman for the U.N.'s World Food Program in Sudan says a six-person Bulgarian helicopter crew has returned to South Sudan and are well a week after they went missing in a conflict-torn area.

Amor Almagro said Sunday the six-member crew was "released," but said she had no further information about who was holding them or how their release was secured.

The helicopter operated by the Bulgarian crew, contracted by the World Food Program, was reported to have made an unexpected landing in a remote area of South Kordofan on the Sudanese side of the border with South Sudan on Monday. Sudanese media reported at the time that rebels operating in the area against the Sudanese government were holding the crew captive.