TORONTO/OTTAWA (Reuters) - The city of Toronto started issuing marriage licenses to gay couples on Tuesday after an Ontario provincial court issued a landmark ruling setting aside the heterosexual definition of marriage.

If the ruling is not appealed, the province of Ontario would be the first jurisdiction in North America to legalize gay marriage. Vermont and Quebec have allowed gay civil unions but not full marriage.

Already a marriage ceremony between two men who had helped bring the case was set for Tuesday afternoon in Toronto, Canada's largest city.

Retroactively, the court decision also recognized two religious gay marriage ceremonies that took place in Toronto in 2001, ordering the province to register those marriages.