|Khalid Sheikh Mohammed was reportedly waterboarded 183 times in March 2003 [Reuters]
Amnesty International has called on Canadian authorities to arrest and prosecute George W Bush, saying the former US president authorised torture in the course of the United States' "war on terror".
Bush is expected to attend an economic summit in Surrey in Canada's westernmost British Columbia province on October 20.
The human rights organisation said in a statement released on Wednesday that the Canadian government has "international obligations ... given [Bush's] responsibility for crimes under international law including torture".
The London-based group also released a 27-page memorandum that it had submitted in September to Canada's attorney general laying out its legal case.
"As the US authorities have, so far, failed to bring former president Bush to justice, the international community must step in," said Susan Lee, Amnesty's Americas director, in the statement.
"A failure by Canada to take action during his visit would violate the UN Convention against Torture and demonstrate contempt for fundamental human rights."
A spokesman for the Canadian government was not immediately available for comment.
Bush cancelled a visit to Switzerland in February after facing similar public calls for his arrest.
Alex Neve, secretary general of Amnesty International's Canadian branch, told a news conference the rights group will pursue its case against the former US president with the governments of other countries he might visit.
"Torturers must face justice, and their crimes are so egregious that the responsibility for ensuring justice is shared by all nations," Neve said.
"Friend or foe, extraordinary or very ordinary times, most or least powerful nation, faced with concerns about terrorism or any other threat, torture must be stopped."
Amnesty, backed by the International Civil Liberties Monitoring Group, said Bush authorised the use of "enhanced interrogation techniques" and "waterboarding" on detainees held in secret by the Central Intelligence Agency between 2002 and 2009.
Bush himself has confirmed he authorised the waterboarding of several individuals.
The detention programme included "torture and other cruel, inhuman and degrading treatment [such as being forced to stay for hours in painful positions and sleep deprivation], and enforced disappearances," Amnesty alleged.
Amnesty's memorandum relies on the public record, US documents obtained through access to information requests, Bush's own memoir and a report from the International Committee of the Red Cross critical of US counter terrorism policies.
The organisation cites several instances of alleged torture of detainees at the Guantanamo Bay naval facility, in Afghanistan and in Iraq, by the US military.
They include that of Zayn al Abidin Muhammed Husayn [known as Abu Zubaydah] and alleged September 11 mastermind Khalid Sheikh Mohammed, both arrested in Pakistan.
The two men were waterboarded 266 times between them from 2002 to 2003, according to the CIA inspector general, cited by Amnesty.