The Obama administration has confirmed for the first time that Hillary Clinton's home server contained closely-guarded government secrets, censoring 22 emails with material requiring one of the highest levels of classification. The revelation comes just days before the Democrats' presidential front-runner competes in the Iowa caucuses. State department officials also said the agency's Diplomatic Security and Intelligence and Research bureaux were investigating if any of the information was classified at the time of transmission, going to the heart of Clinton's defence of her email practices.Republicans have been trying to slow the momentum of Clinton's campaign by playing up her email issues.