Police are making "significant progress" in the investigation into the murder of US journalist James Foley.
Islamic State militants released a video last week appearing to show the journalist's beheading by a masked fighter with a British accent.
Mark Rowley, Metropolitian Police Assistant Commissioner, said the investigation was progressing but declined to give any further details.
"Investigators are making significant progress but we will not be giving a running commentary," Mr Rowley said.
A British family have told ITV News of their devastation after discovering a close relative is fighting with the Islamic State in Iraq.
A French journalist who was held hostage with James Foley in Syria has told ITV News it was "devastating" to see his murder.