Al Qaeda's leader in Iraq called for the kidnapping of Westerners to swap for a Muslim cleric jailed in the United States, according to an Internet audio tape issued on Thursday while at least 22 people were killed in separate incidents of violence across Iraq."I call on every holy fighter in Iraq to strive during this holy month (Ramazan)... to capture some dogs of the Christians so that we can liberate our imprisoned sheikh," said the speaker, identified as Abu Hamza al-Muhajir. He accused US jailers of "torturing" Egyptian cleric Omar Abdel-Rahman, held over links to the 1993 bombing of the World Trade Center in New York. The speaker also called for attacks on US military camps in Iraq using "unconventional bombs such as biological and dirty bombs". The tape's authenticity could not be verified.