"We ask you to withdraw your forces from our land and not to send any more troops, and if not we'll send you this Korean's head," one of a group of armed, masked men standing around the South Korean man said.

The group said South Korea had 24 hours from Sunday night to withdraw its decision last week to send troops to Iraq, al Jazeera said.

A banner in the background named the group as Jama'at al-Tawhid and Jihad, the name of the militant group led by al Qaeda operative in Iraq Abu Musab al-Zarqawi.

The video showed the Korean, who Al Jazeera said named himself as Kim Song Il, shouting violently at the camera: "Please get out of here, here, here. I don't want to die."

South Korea, which already has some non-combat personnel including engineers and medics deployed in Iraq, said Friday it would start to deploy 3,000 troops to the Arbil area in early August to help rebuild the northern Kurdish region.

In Seoul, the spokeswoman for the National Security Council that advises President Roh Moo-hyun said by telephone South Korean officials were checking the report and had no immediate comment. Other officials also had no reaction so far.

There has been vocal opposition in South Korea to Seoul's decision to send troops to Iraq. Roh views the deployment as a crucial gesture to support Seoul's main ally, the United States, which has 37,500 troops in South Korea to deter North Korea.

Beheading prisoners or cutting their throats has been a shock tactic among al Qaeda militants for some time. Last month, Zarqawi's group beheaded American hostage Nick Berg in Iraq. In 2002, Wall Street Journal reporter Daniel Pearl was also beheaded in Pakistan.