Al-Qaida'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 Thursday.

"I call on every holy fighter in Iraq to strive during this holy month (Ramadan)... 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 but it was posted on major websites used by militants.

Al-Qaida in Iraq has killed a number of foreign hostages, some by beheading, in its campaign against US-led forces and the Shi'ite-led Baghdad government.

Muhajir, who replaced slain former leader Abu Musab al-Zarqawi in June, offered a "general amnesty" to Iraqis who had co-operated with US-led forces or fled the country.

"As for those who supported the occupiers and their agents, becoming their eyes and ears, and who betrayed their religion, honor and land for material or social gains ... I declare a general amnesty during this month of generosity and forgiveness," the speaker on the tape said.

"We waive the right to (avenge) the blood that was shed by your hands and your betrayal," he said.

Al-Qaida is one of the main insurgent groups in Iraq and has claimed responsibility for some of the bloodiest attacks.

The voice also said that more than 4,000 foreign insurgents have been killed in Iraq since the US-led invasion in 2003. "The blood has been spilled in Iraq of more than 4,000 foreigners who came to fight," said the man.

(China Daily September 29, 2006)