Baghdad ? The U.S. military on Wednesday accused a Shiite Muslim hard-liner of being responsible for a deadly truck bombing in Baghdad, saying he apparently was trying to provoke a new cycle of sectarian war between Shiites and Sunni Arabs.

The death toll rose to 63 in Tuesday’s blast, which had the hallmarks of an attack by Sunni extremist groups such al-Qaida in Iraq. Residents of the Hurriyah neighborhood had even blamed Sunni politician Adnan Dulaimi, whose guards have been accused of past violence in the capital.

But U.S. military officials said they believed the attack had been carried out by a “special group,” their term for fighters who nominally belong to Shiite cleric Muqtada al-Sadr’s Mahdi Army militia or have broken away. The description, in effect, draws a distinction between the al-Sadr movement’s moderate and more radical elements.