The Papua New Guinea prime minister Peter O'Neill is suing opposition leader Belden Namah and a reporter for defamation.
The move comes after PNG television station EMTV aired allegations by Mr Namah about Mr O'Neill.
Mr O'Neill, in a statement, said he is not only suing Mr Namah for defamation, he will also hold him criminally liable for what he had said.
Mr O'Neill is also suing EMTV journalist Scott Waide and EMTV.
The prime minister said he was shocked by the opposition leader's comments and at the TV network for airing them.
Mr O'Neill said Mr Namah does not have a licence to open his mouth and make wild and unfounded allegations against anyone.
He has to provide evidence or account for what he has said.
This time last year Mr Namah was Mr O'Neill's deputy prime minister, until the two fell out in the lead up to the mid-year national election.
The result of that election saw roughly 94 of PNG's 111 politicians support Mr O'Neill, while Mr Namah currently leads a 14-man opposition.