ST LOUIS, Aug 31 (Reuters) - Republican presidential candidate John McCain, a former prisoner of war in Vietnam, on Sunday issued some of his harshest criticism to date of the use of torture against terrorism suspects during President George W. Bush's administration.

In an interview on Fox News, the Arizona senator laid out his differences with Bush on a number of issues, citing torture as a key sticking point between him and the current president.

"I obviously don't want to torture any prisoners. There is a long list of areas that we were in disagreement on," McCain said of Bush.

Fox interviewer Chris Wallace asked McCain if he was suggesting that Bush did want to torture prisoners.

"Well, waterboarding to me is torture, OK?" McCain responded. "And waterboarding was advocated by the administration, and according to a published report, was used."

Bush has said the United States does not practice torture. But the Central Intelligence Agency has admitted using waterboarding, a form of simulated drowning, and a recent Justice Department probe cited cases of sleep disruption, "short shackling" and other physical techniques against terrorism suspects captured after the Sept. 11 attacks.

McCain suffered torture at the hands of his captors during more than five years in a Vietnam prison camp.

Though a strong advocate of the war in Iraq and Bush's "surge" policy that increased U.S. troop levels there, McCain has been a critic of harsh interrogation techniques against terrorism suspects, including those held at the U.S. military facility at Guantanamo Bay, Cuba.

McCain has clashed with Bush on other issues as well including climate change and high federal spending.

"The first thing we would do is rein in spending," McCain said.