An explosion under a support vehicle at the Dakar rally in Saudi Arabia that injured French race driver Philippe Boutron on December 30 was caused by an improvised explosive device, a French source familiar with the investigation said on Friday. Confirming a report by RTL radio, the source told Reuters that investigators had found traces of explosives on Boutron’s wrecked vehicle in Saudi Arabia. French anti-terrorism prosecutors opened a preliminary investigation into the explosion in January. French Foreign Minister Jean-Yves Le Drian has said that there were suspicions of a terrorist attack…