Gunmen abducted an American teacher on Tuesday from an English language school in Sanaa, capital of wartorn Yemen, witnesses said, in the latest of a series of kidnappings of foreigners.
Armed men in civilian clothes entered the school and forced the teacher into their car as bewildered colleagues and students looked on.
"We were shocked when the armed group entered the building. They got to his office and took him to an unknown location," a Yemeni teacher at the school said.
Local security officials did not immediately respond to a request for comment.
"We are aware of reports of US citizens being held in Yemen. Privacy considerations prevent us from commenting further on this case," a US State Department spokeswoman told Reuters.
Dozens of foreigners were abducted in the years before a civil war erupted in March 2015 when the armed Houthi movement, drawn from Yemen's Zaydi Shia sect, seized Sanaa.
Most were released when their tribal abductors won concessions from central authorities in local disputes, but some have been executed by militants.
A Tunisian employee of the International Committee of the Red Cross was kidnapped in December and appeared in a video pleading for her life last month as a masked gunman stood over her.
The Houthi takeover prompted many countries to close their embassies and aid agencies to sharply reduce their staff, reducing the number of foreigners - and kidnappings - in Yemen.
But over the course of the 18-month-old war several Americans have been detained on espionage charges by the Iranian-allied Houthis, who accuse the United States of arming and supporting a Saudi-led coalition which has intervened in the conflict on the side of the exiled government.
Neighbouring Oman has mediated the release of two Americans held in Houthi custody.