Russia in disarray over missing presidential candidate

"The Moscow prosecutor's office has annulled the decision (of a district prosecutor's office) to open a murder investigation... due to insufficient evidence," said Svetlana Petrenko, a deputy at the Moscow prosecutor's office.

The office had only hours earlier said that a murder investigation had been opened following the disappearance of Rybkin, who has been missing for four days.

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The reversal came apparently at the request of the general prosecutor's office.

"The criminal investigation was opened too early," an official with the general prosecutor's office was quoted as saying by news agencies. "There is currently an investigation into the disappearance of Ivan Rybkin."

Rybkin, whose campaign is financed by Boris Berezovsky, the controversial self-exiled tycoon and President Vladimir Putin's political foe, went missing after he left his apartment in Moscow on Thursday evening.

Mr Berezovsky told the Moscow Times on Sunday that he thought Mr Rybkin would reappear the following day.

"I'm pretty certain he is alive and well," he said, but refused to elaborate.