An insurgent group in Iraq claims to have killed a US hostage who was kidnapped there earlier this week.A video showing security consultant Robert Schulz in handcuffs was aired on an Arabic news channel two days ago. The Islamic Army in Iraq said in an Internet message that it had killed him because Washington did not fulfil its demands which included paying compensation to Iraqis affected by US attacks. A number of other hostages have been captured in Iraq in recent weeks. Christian activist Norman Kember from Britain was kidnapped along with an American and two Canadians in Baghdad two weeks ago. Britain has called on their captors to get in touch. The kidnappers have threatened to kill the hostages unless all Iraqi prisoners are freed. A deadline has been extended until Saturday. A German archaeologist and a French engineer believed to have been kidnapped in Iraq remain unaccounted for.