American and Iraqi troops have captured the man who supervised the bombers of a revered Shiite shrine in Samarra last February, an act that set off a wave of brutal sectarian violence, the Iraqi national security adviser, Mowaffak al-Rubaie, said Sunday.

In a statement broadcast on national television, Mr. Rubaie said the second-ranking leader of Al Qaeda in Mesopotamia, Hamid Juma Faris Jouri al-Saeedi, was captured several days ago as he hid among Iraqi families in a residential building. He said Mr. Saeedi was operating near Baquba, north of Baghdad, in the area where Abu Musab al-Zarqawi, the Jordanian-born leader of the militant organization, had sought refuge before he was killed in an American airstrike three months ago.

Mr. Rubaie described Mr. Saeedi as Al Qaeda's deputy commander in Iraq, serving beneath Abu Ayyub al-Masri, who took over the organization after Mr. Zarqawi's death.