BERLIN (AP) — Three German aid workers have been missing in Syria for 45 days were likely kidnapped, their employer said Saturday.

Gruenhelme e.V. said 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, said a fourth staff member managed to avoid capture and is safe. The kidnapping was kept secret for more than a month so as not to jeopardize the men's safety but all efforts to determine who they are being held by were unsuccessful, he said.

"We're totally in the dark," Neudeck told The Associated Press in a telephone interview. "If the kidnappers wanted a ransom we would have expected to be contacted by now."

German news website Spiegel Online reported that the aid group has been working in northern Syria since September 2012. The region has seen fierce fighting been government troops and rebels seeking to topple the regime of President Bashar Assad.

Gruenhelme e.V., whose name means 'Green Helmets' in German, specializes in reconstructing schools and medical facilities in crisis regions. It has previously sent staff to work in Iraq, Afghanistan and Indonesia.

The German Foreign Ministry didn't immediately respond to a request for comment.