The al-Tawhid wal-Jihad group said in a statement posted on the internet that it had killed the second American, believed to be Jack Hensley, Aljazeera said.

Hensley's reported death comes a day after the group beheaded American Eugene Armstrong who was seized along with Hensley and Briton Kenneth Bigley last week

Zarqawi at par with Osama   

The message, posted on the internet by someone who has in the past posted messages in the name of Tawhid and Jihad, said the group would soon post pictures of the "slaying", the report said.

"The sons of our nation have slit the throat of the second American hostage after the deadline passed [on Tuesday] and we will provide you with pictures soon," the message said.

Meanwhile, in Washington, a US intelligence official said the CIA had determined that the voice on the videotape showing the beheading of the American hostage Eugene Armstrong was most likely that of Zarqawi. "There is high confidence that the voice is indeed of Abu Musab al Zarqawi," a CIA official said

The three captives were employees of a UAE-based building company GSCSGulf  which has contracts with US army bases.