French President François Hollande and UK Prime Minister David Cameron are portrayed as firemen (or, to be non-gender-specific, firefighters) trying to put out the Islamist fire. However, they are only making matters worse, as they are using petrol instead of water.
The cartoon evokes a number of English idioms, all of which have to do with making a bad situation even worse:
• to add fuel to the flames/fire
• to pour petrol/gasoline/oil on the fire/flames
The message seems to be that by using military force in Mali, France, with Britain's aid, has created an even bigger crisis in Algeria. (The hostage takers said that the raid on the Algerian gas facility was in retaliation for French military intervention in neighbouring Mali.)
In Britain, petrol is what you put in your car. Americans use the word gasoline, usually abbreviated to gas. Oil is what comes out of the ground (and what you put in your car engine to lubricate it). For French speakers, petrol is a false friend, since le pétrole is oil.