Kyari was alleged have enjoyed the High Commission to the United Kingdom's financial support with report claiming the Commission paid his medical bills.
Speaking with State House correspondents at the Presidential Villa, Abuja, Onyeama said the report was false.
The minister said: “Because a lot of people do not bring libel cases against media houses, they think they can write whatever they like.
“The report was a blatant falsehood , really defamatory. As we all know, in most of these industrialized countries, if you want medical treatment, or hospital room reserved for you, they will require medical insurance of that country.
“If you do not have, they will require a deposit or a guarantee. Our embassies and high commissions around the world are there to assist Nigerians.
“All that happened in the case of the chief of Staff when he went to the UK for medical treatment was that before he arrived, the High Commission guaranteed that he will pay his hospital bills and that was all.
“A letter was written to the hospital that this person is a high official and we guarantee that he will settle his bill.
“On that basis, they reserved a hospital room for him and afterwards, he settled his bill. During the time he was in London, he never asked the Commission to even provide a car for him. He made his arrangements.
“It is extremely unfair that such defamatory article would have come out. It has no iota of truth in it.
“He had never made any contact with the UK for the one and a half years he has been in office.”
He added that Kyari has not had any contact with the Commission since assumption of office as President Buhari's Chief of Staff.