Yemeni officials say 20 soldiers died when a suicide bomber blew himself up at a military parade drill in the capital Sanaa.
Medical and military officials say the bomber was a soldier who was participating in the rehearsal on Monday at a main square near the presidential palace in Sanaa. It was a practice for the celebration of Yemen's National Day on Tuesday.
Scores of others were also wounded in the attack.
The officials spoke on condition of anonymity because they were not authorized to speak to the media.