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."