The last Soviet leader Mikhail Gorbachev on Thursday slammed the five year jail sentence handed to top Russian opposition leader Alexei Navalny, saying it was unacceptable to use courts to punish political opponents. \"I am convinced that using courts with the aim of fighting political opponents is unacceptable,\" Gorbachev said in a statement posted on the site of his charity. \"Everything I know about this case... unfortunately confirms we do not have independent courts.\"