"Despite the Prime Minister's successful stewardship of Malaysia's economy against global headwinds - as recognised this week by Fitch's upgrade - there have been concerted efforts by certain individuals to undermine confidence in our economy, tarnish the government, and remove a democratically elected Prime Minister," the Prime Minister's Office (PMO) said following media reports alleging the transfer of funds.
"These latest claims, attributed to unnamed investigators as a basis to attack the Prime Minister, are a continuation of this political sabotage," the PMO said in a statement.
"So it is incumbent on responsible members of the media not to accept documents as genuine unless verified by the appropriate authorities," it said.
Meanwhile, the 1Malaysia Development Bhd (1MDB) fund declared that none of its money went to Najib.
"In reference to media reports published earlier today, 1MDB wishes to make clear that the company has never provided any funds to the prime minister.
"To suggest otherwise, as some media outlets have done, is highly irresponsible and a deliberate attempt to undermine the company," it said in a statement.
Najib heads the fund's advisory board.
1MDB is also being probed by the central bank, auditor-general, police force and the parliament's Public Accounts Committee.
