Yemeni rebels have detained seven local employees of a humanitarian aid group and accused them of spying for foreign intelligence, security officials said Friday.

The rebels, known as Houthis, raided a hotel the humanitarian group was using in Ibb province, taking the employees to a prison in the capital, Sanaa.

International Medical Corps said five staff members and two drivers had been detained, and that they were working to secure their release so they could continue to aid a population suffering from war.

"Despite the ongoing conflict that has caused a steady deterioration of humanitarian conditions across the country since 2015, our relief efforts continue to provide a lifeline for families," in several Yemeni cities, said Rebecca Gustafson, a group spokeswoman.

The rebels, from a Shiite sect based in the north, stormed south into the capital in late 2014, leading the president to flee several months later. In March 2015, a Saudi-led coalition launched an air and ground campaign to overthrown the rebels, but it's been unable to advance much from a southern foothold.

The war has fallen into a stalemate, but fighting continues. The U.N. says some 50,000 civilians have been killed or wounded.

The officials spoke anonymously as they weren't authorized to brief journalists.