What is the terror threat in N Africa?

David Cameron says Britain will help to track down and dismantle the terror network responsible for the hostage crisis at a remote gas plant in Algeria.

At least 37 foreigners are now known to have died during the attack, with six British workers feared to be among them.

The BBC's diplomatic correspondent James Robbins looks at how much of a threat is posed by terrorists in North Africa, and what the options are for dealing with them.