Grisly video footage released by the Iran-backed insurgents showed bombed-out buildings with rescue workers lifting bodies from the rubble, mangled corpses left in piles nearby.

"There was a targeting of a detention centre in Saada and currently ICRC teams are inspecting the location to verify the numbers of dead and injured," Basheer Omar, spokesperson for the International Committee of the Red Cross in Yemen, told AFP.

The Saudi-led coalition fighting the rebels did not claim an attack on Saada, the Huthis' heartland.

Separately, a coalition air strike hit a telecommunications hub in the port city of Hodeida. Yemen suffered a nationwide internet blackout, according to web monitor NetBlocks.