Banjul - Gambian President Yahya Jammeh has announced a ban on child marriage in the predominantly Muslim west African nation, threatening heavy jail terms for those who break the new rules.Speaking to a group of Muslim elders, Jammeh said: "From now on child marriage is illegal and is banned in The Gambia. "Anyone who marries a girl under 18 years will spend 20 years in jail. The girls' parents would spend 21 years in jail and anyone who knows about it and fails to report the matter to the authorities would spend 10 years in jail," he added. "The Imam and those that preside over the marriage ceremony would also be sent to jail. If you want to know whether what I am saying is true or not, try it and see."Jammeh instructed lawmakers to pass legislation reflecting the new ban before July 21.Legislators in December passed a bill criminalising female circumcision and introducing prison terms of up to three years for anyone flouting the ban, a month after Jammeh branded the practice outdated and ordered its immediate cessation.Jammeh declared in November that the practice was not required by Islam - the religion of around 95% of the country's 1.8 million population - and that it should be consigned to history, a government spokesperson said.