A second American citizen held hostage in Iraq has been beheaded by his kidnappers, an Islamist website said Tuesday.

Jack Hensley, abducted along with his two colleagues, American contractor Eugene Armstrong and British engineer Kenneth Bigley, was the second to be executed in the past day.

Armstrong was decapitated by the purported al Qaida-linked Tawhid and Jihad (Unity and Holy War) on Monday, as its demand for the release of Iraqi women prisoners in 48 hours had not been met.

The militant group, led by terror mastermind Abu Musab al-Zarqawi, said it would kill the other two if their demand continued to be neglected.

A statement posted on the website said a video footage will be released soon.