combat troops out of afghanistan by the end of 2014, the fight against al qaeda is increasingly turning to yemen. as nbc's chief foreign correspondent richard engel reports, the escalation of violence under scores the new threat. >> reporter: the suicide bomber was disguised as a soldier. he tucked into a crowd at a rehearsal for a military operate in sanai, detonated a bomb and killed nearly a hundred people. yemen's defense minister narrowly escaped with his life and officials say it's likely the work of al qaeda in yemen. while the u.s. has decimated al qaeda elsewhere, the militant group has grown in yemen because the country hasn't had an effective government for a year. but the arab spring finally toppled yemen's former president and the new president is trying to re-establish order and crack down on al qaeda. u.s. military officials tell nbc