An American hostage held in Iraq was beheaded by his captors, CNN reported Monday.

A video posted Monday on an Islamic Web site showed the beheading of the man who was identified as American construction contractor Eugene Armstrong.

The video showed a masked man sawing his head off with a knife.

It also showed the banner of suspected Al-Qaida operative Abu Mussab al-Zarqawi's Tawhid and Jihad group, which said it had kidnapped Armstrong, along with another American hostage Jack Hensley and British engineer Kenneth Bigley, in central Baghdad last Thursday.

Tawhid and Jihad said in footage posted on the Internet on Saturday it would kill the three hostages unless Iraqi women were freed from Abu Ghraib and Umm Qasr jails in 48 hours.

The group threatens to kill the remaining hostages unless their demand was met.

Zarqawi's Tawhid and Jihad group has claimed responsibility for most of the suicide bomb attacks in Iraq since the fall of Saddam Hussein. It has already beheaded several hostages.