WASHINGTON (Reuters) - U.S. President Barack Obama was not surprised that al Qaeda bomb makers were still determined to attack civilians, he said in a television interview that aired on Thursday, days after reports of a foiled airplane suicide bomber plot in the Middle East.

Obama told ABC News in an interview taped on Wednesday that he was briefed on the would-be suicide mission in April, adding that officials stayed on top of the situation and that lives and airplanes were never at risk.

"I don't think it should be any surprise. I've been very clear that - even with the death of (Osama) bin Laden, even as weakened as Al Qaeda is - if you have a bunch of extremists who are adamant about trying to kill civilians than we are going to have to maintain constant vigilance and create a whole series of layers of protection and barriers," he said in an interview.

"We were on top of this the entire time. At no point were American lives in danger or American aircraft in danger," he added.

Details emerged earlier this week about the plot, which involved a would-be suicide bomber who was planted in al Qaeda's Yemeni affiliate by an allied intelligence agency or turned into an informant early in the conspiracy.

Obama said while security experts were able to foil the plot and that the nation's law enforcement, military and intelligence officers have continued to improve, that officials would have to continue to remain vigilant to protect the public.

"It's an indication of success, but it's not a reason to be complacent," he told ABC in a wide-raging interview that also made news for Obama's support of gay marriage.

(Reporting by Susan Heavey; Editing by Paul Simao)