Russia's election authorities said Monday they may reject the presidential candidacy of liberal opposition leader Grigory Yavlinsky after finding alleged violations in his registration forms.
The 59-year-old economist immediately blamed the threat on Prime Minister Vladimir Putin and vowed to fight for his right to challenge the overwhelming favourite in the 4 March ballot.
"I think that Vladimir Putin is the one who makes these decisions," Yavlinsky told reporters. "Who else would make them?"
The veteran Yabloko party chief made a surprise return to Russian politics last year after refusing to face Putin or his hand-picked successor Dmitry Medvedev in two past polls that he termed undemocratic.
He needed to gather two million signatures to qualify for elections against Putin -- an ex-KGB agent who hopes to return for a historic third term -- because his party failed to make it to parliament in December polls.
A top election official said nearly a quarter of the signatures submitted by Yavlinsky had problems in the first sample of papers examined thus far.
"The number of questionable and invalid signatures stands at 23.07 per cent" in the first sample of 200,000 signatures, elections commission member Nikolai Konkin was quoted as saying by the state news agency ITAR-TASS.
Independent candidates are disqualified if mistakes are found in five per cent of the signatures. Officials said they would conclude a second probe by the end of the week.
The election commission separately reported that it was on verge of registering the candidacy of billionaire tycoon Mikhail Prokhorov because he only had problems with about four percent of the signatures.
The precious metals magnate - who like Yavlinsky has voter approval of less than five percent - has been trying to dispel suspicions he was running at the Kremlin's behest to make Putin's seemingly inevitable victory look competitive.
Prokhorov said Yavlinsky's potential removal would hurt Russia's reputation and called for the authorities to scrap the mandatory signatures rule.
"I think the removal of Yavlinsky is a blow to the legitimacy of the elections of the president of Russia," Prokhorov told reporters.
"I am for political competition, for the freedom of participation by all parties and all citizens of the Russian Federation who want to take part."
Yavlinsky said the problems were not actually with the signatures but the forms on which they were written. Yabloko said it used photocopies of the official form in some far-flung regions because of logistical problems.
"This is a purely political decision that has nothing to do with specific signatures or anything else of the sort," Yavlinsky told reporters.
"The situation with the 4 March elections is now even clearer," he added.
Yavlinsky was one of the most high-profile politicians of the Boris Yeltsin era when he fought bitterly against the "shock therapy" reforms of the 1990s.
He always promoted more socially-oriented policies than early post-Soviet economists like Yegor Gaidar and staunchly refused to form alliances with other liberal leaders of the era.
The one-time boxer resumed the leadership of the Yabloko party in November after initially stepping down after it lost its remaining four seats in the 450-seat lower house in 2007 elections.