The French army regards a photograph of one of its soldiers in Mali shown posing in a skeleton mask as "unacceptable" behaviour, a military spokesman said Monday.

"This is unacceptable behaviour," Colonel Thierry Burkhard told a press conference.

The image, which has spread widely on the Internet, was "not representative of the action that brought France to Mali to help" or of that which soldiers carried out "putting their lives in peril", Burkhard said.

Taken by AFP photographer Issouf Sanogo, the photograph shows a soldier at Niono, in central Mali, hiding his face from desert sand using a scarf that resembles a death mask. It is reminiscent of a character in the popular combat video game Call of Duty.

The army was working to identify the soldier, Burkhard said.