Rybkin's account to journalists in London was the third time he had tried to explain why he had gone off to Kiev without telling his wife or campaign aides, triggering a police manhunt, and what he did before he resurfaced five days later.
On his return to Moscow, Rybkin, a harsh critic of President Vladimir Putin, initially said he had been with friends, but later told an interviewer he had feared for his life and gone into hiding for part of the time in the Ukrainian capital.
On Friday, Rybkin said he had gone to a Kiev flat in the company of strangers who said he would be meeting Chechnya's fugitive president Aslan Maskhadov.
Safety of family
He awoke after a time to find himself alongside two armed men who showed him and others in "disgusting" video films intended to compromise him.
"All my statements in recent days in Kiev and in Moscow do not reflect the reality and were forced. I was trying to ensure the safety of my family and myself," he said.
"I don't know who did it, but I know who would benefit from it"
presidential candidate, Russia
"I don't know who did it, but I know who would benefit from it. It benefits those who want to compromise and humiliate the opposition," Rybkin said.
Like five other challengers running in the 14 March contest, Rybkin is unlikely to score more than a few percentage points against the widely popular Putin. Moscow media have reacted with incredulity to earlier explanations of his disappearance.
Rybkin, a former speaker of parliament and negotiator with Chechen separatists, said he decided during his captivity he would remain in the presidential race come what may.
"I decided that I didn't care about my reputation or whatever might happen to me and that I would do all I could to prevent all those incompetents and President Putin from destroying my country," he said.
"From today I am launching an election campaign from here, from abroad," he added.
Rybkin has been backed by exiled tycoon Boris Berezovsky, who launches periodic attacks on Putin from his base in Britain, where he has been awarded political asylum.
Rybkin said he would remain in western Europe until after the elections to ensure the safety of his family. But unlike Berezovsky, he had no intention of seeking asylum and pledged to return to Russia whatever the result of the election.