The Defense Department said Abdallah Salih al-Ajmi, 29 -- who the U.S. military claimed fought with the Taliban in Afghanistan and was detained for three years -- was involved in one of three April 26 suicide bombings in which seven members of the Iraqi forces in Mosul were killed, The Washington Post reported Thursday.

Ajmi was at Guantanamo until late 2005, when he was transferred to the custody of the Kuwaiti government.

Military officials said Ajmi's motives weren't known, but in an audio recording, he implored listeners to participate in suicide bombings attacking Americans.

"Whoever can join them and execute a suicide operation, let him do so. By God, it will be a mortal blow," Ajmi said in the tape translated by SITE Intelligence group in Bethesda, Md.

The suicide bombing is the first attack in Iraq tied to a former Guantanamo detainee, the Post said. The Defense Intelligence Agency estimated as many as three dozen onetime detainees are either confirmed or suspected to have returned to terrorist activities, an estimate disputed by international human rights groups and attorneys representing Guantanamo inmates.