Charlie Haughey was warned by loyalist paramilitaries that MI5 ordered his assassination, declassified state papers have revealed.
Records from his office while he was taoiseach in 1987 reveal that the UVF wrote to him to tell him that British intelligence also launched a smear campaign against him.
The loyalists claimed their organisation was used by MI5 and MI6, backed up by British Army special forces, from 1972 to 1978 and again in 1985.
"In 1985 we were approached by a MI5 officer attached to the NIO (Northern Ireland Office) and based in Lisburn, Alex Jones was his supposed name," the UVF said.
"He asked us to execute you."
The previously secret letter, on UVF headed paper, showed the loyalists told Mr Haughey that the MI5 operative gave details of his cars, photographs of his home, his island, Inishvickillane, and his yacht, Celtic Mist.
The paramilitaries also claimed to have been given details of Mr Haughey's trips to Farranfore airport in Kerry and photos of a plane he used.
"We refused to do it, we were asked would we accept responsibility if you were killed we refused," the UVF said in the letter.
Mr Haughey was on holiday when the letter arrived in August 1987.
He was shown it later and, according to a handwritten note on another document from his office, he asked for the Department of Justice to let him know if they had any information.
The UVF also claimed MI5 planned to supply a spoon of "Anthras" (sic), "Foort and Mouth Disease" (sic), "Fowl Pest, Swine Fever, and Jaagsikpi" to anyone who would release them in Ireland.
The loyalists said the plot was to destroy the "Eire economy".
In the letter, the UVF said it had killed 17 men using information from British intelligence.
Signed in block capitals "Capt W Johnston", the name used by the UVF in all its formal statements, it closed with the line: "We have no love for you but we are not going to carry out work for the Dirty Tricks Department of the British."
The documents can be seen in the National Archives in file 2017/10/34 from the Taoiseach's office.