SANAA, Yemen -- Yemeni security officials say seven Houthi rebel prisoners have been released by Saudi Arabia and returned to the capital, Sanaa. It's the first small prisoner exchange between the two sides, after the rebels released a Saudi a day earlier.

The rebels were transferred by the International Red Cross late on Wednesday, and the aid group had also arranged for the transfer of the Saudi prisoner. The Houthis had said they were releasing him because he's sick.

U.N. Special Envoy Martin Griffiths welcomed the move, the first since a Saudi-led coalition intervened in 2015 in Yemen's civil war to fight the rebels.

Griffiths posted on social media that he "hopes this will give a push to the rapid implementation of the prisoner exchange agreement" struck in Stockholm in December.