Yemeni security officials said Houthi rebels have detained seven local employees of the International Medical Corps, accusing them of spying for foreign intelligence.
They said the Houthis raided a hotel the humanitarian group was using in Ibb province, taking the employees to a prison in Sanaa.
Meanwhile, three suspected Al-Qaeda members were killed overnight in what local officials believed was a US drone strike in southern Yemen.
Residents and local officials said on Friday the attack took place in Mozno in Al-Wadie district of Abyan province.
The three killed included the local leader of the militant group, Waddah Muhammed Amsouda, who was meeting the others in a house in the area, they said.
Residents also reported a separate attack on a suspected Al-Qaeda vehicle, in the same province, but said the number of casualties was unknown.
Yemen has been wracked by chaos since late 2014, when the Houthis and their allies overran Sanaa and other parts of the country, forcing President Abd Rabbuh Mansour Hadi and his Saudi-backed government to temporarily flee to Riyadh.
The Saudi-led coalition began a military campaign against Iran-backed Houthi militias in March 2015. It sides with the President Abd Rabbuh Mansur Hadi, while the Houthis are aligned with ousted President Ali Abdullah Saleh, who was ousted after Yemen revolution in 2012.