United States presidential hopeful Ted Cruz has been accused of telling a "whopper" after he claimed sexual assaults on women in Australia increased significantly following the 1996-97 gun buyback scheme.

Senator Cruz said on high-profile American radio host Hugh Hewitt's show on January 12 that Australia's post-Port Arthur massacre gun legislation meant women were unable to defend themselves from being raped.

"And as you know, Hugh, after Australia did that [gun buyback program], the rate of sexual assaults, the rate of rapes, went up significantly, because women were unable to defend themselves," Senator Cruz told the radio host.

"There's nothing that criminals or terrorists like more than unarmed victims."

The Washington Post's Fact Checker column has examined Senator Cruz's comment and rated it a "whopper" of a factual error, the highest rating on its "Pinocchio Test".

The Post analysis found no significant spike or drop, but a gradual increase in sexual assault rates over the decade after the gun buyback scheme came into effect.

The increase was likely affected by a rise in the reporting of sexual assaults and there was not prevalent use of handguns for self-defence before 1996, as Senator Cruz suggested, the newspaper concluded.

"The rates didn't go up 'significantly' after the buyback and there's no evidence changes to gun laws in Australia affected sexual assault rates or jeopardised the ability of women to protect themselves," the Washington Post told readers.

The newspaper also concluded that given gun culture in Australia and the US is not comparable, including carrying concealed guns and the ability to carry firearms for self-defence, "politicians should refrain from attributing good or bad changes in Australian crime rates to the buyback program or to the legislative package".

"We also warn politicians on both sides of the gun debate about making broad assertions about Australia to justify policy arguments for the United States," the Post concluded.

The graph shows rates of reported sexual assaults in Australia after the large-scale gun buyback in 1996-7. ( Sourced: Australian Bureau of Statistics and Washington Post )

The newspaper spoke to Samara McPhedran, senior research fellow at Australia's Griffith University and chair of the International Coalition of Women in Shooting and Hunting.

The Post also examined research by the Harvard Injury Control Research Centre, the Australian Institute of Criminology, Australian Institute of Health and Welfare, the Law Library of Congress, Christine Neill, economics professor at Canada's Wilfrid Laurier University and Australian MP Andrew Leigh, a former Australian National University economics professor.

Conservative candidate Senator Cruz is Donald Trump's biggest rival for the Republican presidential nomination.

The gun debate has become a hot button issue in the presidential race, with Republican candidates like Senator Cruz and the National Rifle Association attacking President Barack Obama and Democrat hopeful Hillary Clinton's references to Australia's firearm laws.

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AAP