An Islamic Web site has posted images and videos of what it says is the killing of 12 Nepalese hostages by a militant group in Iraq.

The footage showed one being beheaded and the rest apparently being shot from an assault rifle at the back of the head.

"We have carried out the sentence of God against 12 Nepalese who came from their country to fight the Muslims and to serve the Jews and the Christians ... believing in Buddha as their God," said a statement on the site by Jaish Ansar al-Sunna.

"America today has used all its force, as well as the help of others, to fight Islam under the so-called war on terror, which is nothing but a vicious crusade against Muslims," the statement said.

The claims came as another Islamic group held two French journalists hostage, threatening to kill them unless France revokes a law banning Muslim children from wearing headscarves in public schools.