A German aid group says three of its staff have been missing in Syria for 45 days and were likely kidnapped.

Gruenhelme e.V. says Bernd Blechschmidt, Ziad Nouri and Simon S., whose last name wasn't provided, were taken by unknown persons from the town of Harem in Idlib district on May 14.

The group's founder, Rupert Neudeck, told The Associated Press on Saturday that a fourth staff member managed to avoid capture and is safe.

Neudeck says the aid group kept the kidnapping secret so as not to jeopardize their safety but all efforts to determine who they are being held by were unsuccessful.

Gruenhelme e.V., whose name means 'Green Helmets' in German, specializes in reconstructing schools and medical facilities in war zones.