No files relating to Jeremy Corbyn have been found in the archives of the Stasi security service of the former East Germany, a German official has confirmed.
The Federal Commission, which looks after the Stasi archives, took the unusual step of announcing it had found no records relating to Mr Corbyn following days of press speculation about the Labour leader's links with former communist states.
A spokesman for Mr Corbyn warned that inaccurate comments by press and political opponents about his sympathies may put his personal security in danger.
And lawyers acting for the Labour leader have written to Conservative vice-chairman Ben Bradley threatening court action unless he apologises over a tweet linking him with communist spies.
The letter also calls on the Mansfield MP to pay Mr Corbyn's legal costs, make a donation to charity in lieu of damages and provide a written undertaking not to repeat what the lawyers describe as a defamatory statement.
In a statement responding to press speculation, Dagmar Hovestaedt, a spokeswoman for the Federal Commissioner for the Stasi Records in Berlin, said: "The most recent researches in the written records of the Ministry for State Security of East Germany have not produced any records or any other information on Jeremy Corbyn or Diane Abbott."
In a video message on Tuesday, Mr Corbyn accused newspapers of spreading "lies and smears" about his alleged links with a Czech intelligence agent in the 1980s, and warned media barons that "change is coming" if Labour wins power.
Mr Corbyn's spokesman told reporters that Finsbury Park attacker Darren Osborne - jailed for life last month for driving a van into a crowd outside a north London mosque - had said the Labour leader was his intended target because of his supposed support for terrorism.
The case "highlights the serious dangers of the use of language in some of the reporting and the language used by politicians around Jeremy's leadership, and the importance of framing completely legitimate political debate in ways that don't incite hatred and violence", said the spokesman.
"The constant repetition both by Government politicians and sections of the press portraying Jeremy Corbyn as a terrorist sympathiser or as in some way an apologist for terror - which is entirely false - has dangers to it which have been quite clearly demonstrated. There needs to be an awareness of the dangers of using that kind of language."
He denied that Mr Corbyn's comments suggested he would clamp down on the free press, insisting Labour was committed to a review aimed at opening up media plurality.
Meanwhile, the spokesman challenged records of supposed meetings between the then Labour backbencher and the former agent of the Czech StB intelligence agency Jan Sarkocy.
Mr Corbyn recalled speaking to a diplomat from the then communist country in 1986, as one of many meetings with ambassadors, politicians, activists and dissidents from "the majority of countries in the world", said the spokesman.
But another meeting with the same man was recorded in StB files as taking place the following year in the House of Commons, on a Saturday when the Labour MP's own diaries record he was attending a conference in Chesterfield.
Theresa May sought to make capital out of reports of Mr Corbyn's supposed Cold War links at Prime Minister's Questions in the House of Commons.
Mrs May said the Labour leader normally used his question to ask her to "sign a blank cheque", adding: "I know he likes Czechs."
Mr Corbyn appeared to pretend to yawn following the joke.