New Zealand First leader Winston Peters is accusing the Prime Minister of spying on him with the Government Communications Security Bureau.
John Key on Wednesday accused Mr Peters of meeting internet entrepreneur Kim Dotcom three times.
Mr Peters on Thursday confirmed meeting Mr Dotcom three times over two years, but said he had agreed to keep them confidential.
He told reporters that the only way John Key could know about them was if he was being spied on.
"What's his informant, who is he? ... This is is a surveillance matter and I want to know more about it."
John Key on Thursday denied using the GCSB to keep tabs on Mr Peters. He wouldn't say who told him, but said it definitely wasn't a spy agency.
"I heard from an individual who's a person who's got nothing to do with National Party, nothing to do with any government agency. The person told me it was three. I was pretty sure they'd be right - because they often are - and guess what, they were."
Mr Peters said he first met Mr Dotcom to discuss his move to New Zealand and then twice more to discuss the GCSB case.
Nothing was asked for or offered, and no taxpayers' money was used, he said.