“In Islam, making the difference is not based on civilians and military, but on the basis of Muslims and infidels,” said the voice attributed to the fugitive leader who has a 25-million-dollar price on his head.

“The Muslim’s blood cannot be spilled whatever his work or place, while spilling the blood of the infidel, whatever his work or place, is authorized if he is not trustworthy,” said the tape, whose veracity could not be determined.

The recording comes a day after US officials claimed to have seized a letter allegedly sent to Zarqawi by Al Qaeda number two Ayman Zawahiri, in which he raised concerns over the impact on Arab opinion of videotaped executions.

Zarqawi, a Jordanian-born Islamist extremist, is Iraq’s most wanted man.

His Al Qaeda Group of Jihad in the Land of Two Rivers has claimed responsibility for some of the most gruesome attacks in Iraq, including the beheadings of foreign hostages and Iraqis.