PARIS, April 2 (Reuters) - A man and three minors have been put in pre-trial detention as part of investigations into a foiled March bomb attack on the Bank of America's Paris office, authorities said - a plot that officials say may be linked to a pro-Iranian group.The explosive device was the most powerful of its kind discovered in France and "could have generated ... a powerful fireball several metres in diameter and spread a fire," the anti-terrorism prosecutor said late on Wednesday.