A second Frenchman who appeared among Islamic State jihadists in a grisly execution video has been identified as a man from an eastern suburb of Paris, a source close to the case said Wednesday.

President Francois Hollande earlier confirmed a second Frenchman was spotted in the video, who the source said went by the name Abu Othman and originated from Val-de-Marne.

He was seen in a video released Sunday by the IS group which showed the killing of 18 Syrian prisoners and a US aid worker.

French prosecutors had already confirmed the identity of one man in the video, 22-year-old Maxime Hauchard from Normandy in northern France.

Hollande said it was not clear exactly what role the men played in the beheadings. "The judicial system will have to establish this," he told a news conference during a visit to the Australian capital Canberra.

French Interior Minister Bernard Cazeneuve said in Paris that Hauchard left for Syria "in August 2013 after a stay in Mauritania in 2012", after reportedly becoming radicalised online.

Around 1,000 French nationals are thought to have taken part in the conflict in Syria and Iraq, with 375 currently there, the government has said. At least 36 have died.

Hollande said the issue of foreign fighters and how they were being "brainwashed" was a major concern.