ABOARD THE PAPAL PLANE — In an offhand remark on the papal plane en route to Mozambique, Pope Francis on Wednesday acknowledged the sharp opposition he has faced from conservative Catholic detractors in the United States, calling it an “an honor that the Americans attack me.”

His remark came at the start of a six-day trip to Africa, as Francis shook hands in the back of the plane with a French reporter who handed him a copy of his new book, “How America Wanted to Change the Pope.”

Francis warmly told the reporter, Nicholas Senèze, who covers the Vatican for the French Catholic newspaper La Croix, that he had been unable to find the book, which explores American financial, political and media backing of the small but noisy conservative opposition seeking to undermine Francis. Apparently referring to his critics, Francis quipped that their disapproval is “an honor.”

He then handed the book to an aide, and jokingly called it “a bomb.”

Francis’ priorities and inclusive approach to the papacy have infuriated some American prelates, donors and their supporters in the constellation of conservative Catholic media. Those critics often complain that Francis is watering down church orthodoxy, retreating in the culture wars and sowing confusion in the church.