An internet audio tape issued on Thursday identifies the speaker as Abu Hamza Al-Muhajir.
He’s urged militants in Iraq to step up their jihad, or holy war, during the Muslim fasting month of Ramadan.
The tape also claims more than four thousand foreign fighters have been killed in Iraq, while fighting US-led forces and the Baghdad government.
The tape accuses US jailers of torturing Egyptian cleric Omar Abdel-Rahman, who was found guilty in 1995 of conspiracy to attack US targets, including the 1993 bombing of the World Trade Centre in New York.
Muhajir is an Egyptian also known as Abu Ayub Al-Masri.
He issued an audiotape at the beginning of September urging followers to kill Americans, which US commanders in Iraq believe has contributed to an increase in attacks on their troops.