The US defence secretary Leon Panetta opened his speech to an audience in London by warning terrorists in Algeria that there was "no place to hide".
He said that American authorities were working closely with Britain and other nations "to assess precisely what was happening on the ground."
He added that "regardless of the motivation of hostage takers there was no justification for the kidnap and murder of innocent people going about their daily lives".
He said: "Terrorists should be on notice that they will find no sanctuary or refuge; not in Algeria, not in North Africa, not anywhere.
"Those who will want only to attack will have no place to hide."
David Cameron warned that north Africa is becoming a "magnet for jihadists" as he announced help to tackle the terror threat in the region.
A British man from Aberdeenshire has spoken to ITV News about his dramatic escape from militants and his concern for some of his colleagues.
Stephen McFaul, one of dozens of hostages taken by Islamist fighters at gas plant in Algeria, is due to arrive back in Belfast later today.