Portugal's foreign ministry has asked Baghdad to lift the diplomatic immunity of the Iraqi ambassador's teenage sons who are suspected of attempted homicide.

The foreign ministry said in a statement it conveyed the request to the Iraqi charge d'affaires in Lisbon on Thursday.

The Portuguese attorney-general's office says investigators suspect the ambassador's twin 17-year-old sons in the brutal beating last week of a 15-year-old Portuguese boy, who spent five days in a coma. He has severe facial and skull fractures.

The Iraqi teenagers have admitted to Portuguese media they assaulted the boy during night-time fighting with local youths in a rural town in northeastern Portugal.

The attorney-general's office wants the boys' immunity lifted so they can be interrogated by detectives.