"We are working to ensure this matter can be resolved as soon as possible," the Los Angeles-based relief agency said in a statement posted on Friday on its website.
The non-governmental organisation declined to reveal further details today, but a Yemeni aid official told AFP that the detained staff are all Yemenis, and were captured in the central province of Ibb.
The organisation's website says it has more than 150 local staff in Yemen and that it has operated since 2012 from three offices in the Arabian Peninsula country.
Shiite Huthi rebels and their allies control most of Yemen's north and west, while forces loyal to President Abedrabbo Mansour Hadi, backed by a Saudi-led Arab coalition, control the south and east.
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Humanitarian agencies have long complained of the lack of access to people in dire need for help in war-torn Yemen.
The UN says seven million people face serious risk of famine unless international donors intervene, and has called for USD 2.1 billion in humanitarian aid.
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