Boris Johnson has admitted he doesn't know how many Russian oligarchs are pumping "serious money" into the Conservative Party.
And the Prime Minister defended the government's decision to sit on a report into Russian interference in UK democracy until after the election, insisting there was "absolutely" nothing to hide.
Asked if media reports were correct that around nine Russian oligarchs were donating "serious money" to the Tories, Mr Johnson told BBC Radio 5 Live: "I don't know."
He added: "They have all been properly vetted. They all... and, it's open to... these, these donations are all open to challenge if people think that they are not fit and proper persons, then they are not allowed to donate. That's the rule.
"But, I don't think that we should be hostile to people simply because of the country that they come from. It is very important that we show balance and fairness in this."
Pressed on why the Intelligence and Security Committee's report into possible Russian meddling had not yet been published, Mr Johnson said: "Because I see absolutely no reason to change the normal procedures for publishing ISC reports, just because there is an election.
"Because they are not normally published at that pace and... there is no reason to change the procedures."
Asked if there was anything to hide in the report, the PM said: "Absolutely not."
Pressed on the possibility of Russian interference in the UK democratic process, Mr Johnson said: "There is no evidence for that and I think that you have got to be very careful before you simply cast aspersions on everybody who comes from a certain country just because of their nationality."
Former US secretary of state Hillary Clinton has expressed concern that the ISC report has not been released.
She told the Guardian this week it was "incredibly surprising and unacceptable that in your country there is a government report sitting there about Russian influence and your current Government isn't releasing it".
Ms Clinton added: "I mean, who do they think they are that they would keep information like that from the public, especially before an election?
"Well, I'll tell you who they think they are. They think that they are the all-powerful, strong men who should be ruling."
The chairman of the ISC, former Tory attorney general Dominic Grieve, has expressed concern about the delay in publishing the report on possible Russian interference in UK politics.
