An audio tape allegedly from al Qaida ally Abu Musab al-Zarqawi called on insurgents in Iraq to attack US supply lines to prevent US-led forces from attacking other cities after Fallujah, Sky News TV reported Monday.

The authenticity of the tape, posted on an Islamic Web site, could not be verified immediately.

"The enemy is now avoiding fighting you for fear of dispersion and attrition. It has massed its capabilities to finish off Islam in Fallujah. If it finishes Fallujah, it will move in you direction. Beware and deny it the chance to carry out this plan," said the speaker.

"Shower them with rockets and mortars and cut all the supply routes," he added.

The US military said Sunday some 1,200 insurgents have been killed in the offensive against Fallujah since it began on Nov. 7, adding 450 to 550 were captured.

However, Iraqi officials said they believed al-Zarqawi, whose group was believed to be based in Fallujah, had escaped.

The US military and the interim Iraqi government vowed to retake the key rebel stronghold to pave way for the general elections slated for January.