Rodrigo Duterte, the Philippines' president, pauses during an event with the Filipino community in Singapore, on Friday, Dec. 16, 2016.

Philippine President Rodrigo Duterte derided U.S. ambassadors as "spies" on Thursday, responding to a media report of an alleged American plot to destabilize his government, a job he said some envoys were appointed solely to do.

The volatile former mayor said though had received no intelligence reports of any U.S. plan to undermine his presidency, he believed most ambassadors were in cahoots with the Central Intelligence Agency (CIA), which had a track record of meddling in other countries' affairs.

The Manila Times newspaper on Tuesday reported a former U.S. ambassador to the Philippines had prepared a "blueprint to undermine Duterte", citing a document it had received from a what it described as a "highly placed source".

The U.S. State Department has described the allegations as "false".

"Most of the ambassadors of the United States, but not all, are not really professional ambassadors. At the same time they are spying, they are connected with the CIA," Duterte said in a television interview.

"The ambassador of a country is the number one spy. But there are ambassador of the U.S., their forte is really to undermine governments."