The Central Intelligence Agency (CIA) will not bring back torture to make captured terrorist suspects talk, a former CIA chief said, adding that if Donald Trump becomes U.S. president and subsequently orders the spy agency to waterboard terrorists, he has "to bring his own damn bucket."

Speaking to NBC News, former CIA director Michael Hayden noted that Trump, the likely Republican presidential nominee, has vowed to bring back torture if he wins the White House.

However, Hayden said CIA officials, both former and current, would refuse to heed any such orders even from the President considering what happened when its post 9/11 interrogation programme was exposed.

"Multiple investigations, grand juries, presidential condemnations, and congressional star chambers have a way of doing that to you," said Hayden, who was CIA director at the end of the George W. Bush administration.

Referring to Trump, Hayden then said, "if you want somebody waterboarded, bring your own damn bucket."

Trump said Wednesday he is convinced that "torture works" and that he intends to bring back waterboarding and even "much stronger" methods.

The U.S. should respond to the grisly brutality being shown by the Islamic State (ISIS) in kind, he said.

"Believe me, it works," Trump said. "And waterboarding is your minor form. Some people say it's not actually torture. Let's assume it is. But they asked me the question: What do you think of waterboarding? Absolutely fine. But we should go much stronger than waterboarding. That's the way I feel. They're chopping off heads. Believe me, we should go much stronger, because our country's in trouble. We're in danger. We have people that want to do really bad things!"

Other Republican presidential candidates—including Senators Marco Rubio and Ted Cruz—are not ruling out bringing back harsh techniques although none has been as detailed as Trump in describing those techniques.

Polls show that a majority of Americans think the treatment of terror suspects by the CIA was justified.

But CIA officials, including some who played key roles in the post-9/11 terrorist detention programme, say the fallout from that controversial episode has left the spy agency unwilling ever again to conduct coercive interrogations. That would be true, they say, even if the country was attacked again and Congress undid the law it passed last year banning harsh techniques.

The CIA last conducted brutal interrogations on al Qaeda operatives after the 9/11 attacks, including the simulated drowning technique known as waterboarding, which was used on 9/11 mastermind Khalid Sheikh Mohammed and two others. Other coercive techniques included sleep deprivation, slapping, humiliation, nudity, fear and isolation, often used in combination.

The CIA personnel who supervised and carried out the so-called "enhanced" interrogations on prisoners at secret sites abroad after the Sept. 11 terror attacks were subject to lengthy criminal investigations that required them to hire personal lawyers. The U.S. Senate accused the CIA of repeatedly lying about the nature and effectiveness of the techniques. Some CIA personnel were publicly pilloried.

This happened despite the fact that the interrogation programme was ordered by President Bush and sanctioned by Justice Department lawyers.

The chastised CIA officers involved vehemently disagreed with the U.S. Senate report and they feel betrayed, NBC News said.

They feel that they did what was asked of them to stop terrorism, and after "the political winds changed, they were vilified as 'torturers' and 'war criminals' — just for doing their thankless and dangerous jobs to keep the country safe," according to John Rizzo, a former CIA lawyer.

"And now, under a Trump administration," said Rizzo, "many of these same CIA career officers would be ordered to go down—perhaps double down—on that perilous path again? Who could blame them for refusing to expose themselves and their families to a reprise someday of the ordeal they have had to endure?"

President Obama banned the techniques when he took office, and Congress last year enshrined that ban into law.