TORONTO - Ontario's highest court has ruled that a three-year mandatory minimum sentence for possessing a loaded prohibited gun is unconstitutional.

The Ontario Appeal Court ruling strikes down a plank of the federal Conservatives' 2008 omnibus bill.

The court found a three-year prison sentence for a first offence of the gun crime is "cruel and unusual punishment."

The court says the ruling has no significant impact on sentences for people engaged in criminal conduct or who pose a danger to others, saying they should continue to receive sentences to emphasize deterrence and denunciation.

The Appeal Court heard six appeals together in February because each involved a constitutional challenge to a mandatory minimum sentence for various firearm offences.

Federal government lawyers had argued in support of the law, raising a spate of gun violence in 2005, which first prompted Ottawa to propose the stiffer penalties.