UNITED NATIONS (AP) — The United Nations says two workers in South Sudan remain missing after groups of armed men seized several people at an airfield in recent days.

A statement Friday by the U.N. mission in South Sudan said an armed group of 15 to 20 people abducted three contractors for the mission at the airfield in Malakal on Oct. 10. Two were released the next day, but the third is still missing.

And on Thursday, another armed group seized a worker with the World Food Programme as he was boarding a U.N. flight at the airfield. The U.N. statement says he is still missing.

The U.N. mission in South Sudan says it is engaging both the South Sudan government and militia groups to win the workers' release.