In late May, Russia's opposition nominated Vladimir Bukovsky, 65, who spent a total of 12 years in Soviet prisons, to run for the presidency.
But Bukovsky said some legal obstacles, such as his lack of a Russian passport and a failure to meet the constitutional requirement that candidates live in Russia for at least a decade before being nominated, could prevent him from running.
In 1992, President Boris Yeltsin returned Bukovsky's citizenship, but the former dissident sent the passport back in a demonstrative gesture.
He said that he was likely to turn to the Constitutional Court to resolve his legal problems.
Bukovsky said he hoped the campaign he had decided to begin would help unite the opposition in Russia, which is "weak and in decay."
Bukovsky was imprisoned several times for organizing poetry meetings in central Moscow and the first demonstration in 40 years in the early 1960s.
In 1970, he managed to smuggle evidence of the use of Soviet psychiatric hospitals as prisons to the West. In 1976, Bukovsky was exchanged for former Chilean Communist leader Luis Corvalan in Switzerland.
Bukovsky, who has lived in Cambridge doing neurophysiology research and publishing books since 1976, came to Moscow in 1991 during Boris Yeltsin's campaign for presidency as an expert to testify at a Communist Party trial.
He was considered a potential vice presidential running mate for Yeltsin. He has also been offered a chance to run for mayor in post-Soviet Moscow, but refused.
President Vladimir Putin, who has been increasingly criticized in the West for his anti-democratic record but who remains popular inside Russia, has repeatedly denied the possibility of his staying in office for a third term, but is widely expected to name his successor, who is likely to win polls in the March 2008 elections.
