The former world chess champion Garry Kasparov has announced that his participation in the Russian presidential race was over before the official campaign period had even started.
"My presidential campaign will finish tomorrow," he said. "There is no hall in Moscow where my initiating group can meet."
According to Russian law, potential candidates must gather 500 supporters in order to begin the process of standing for president, and inform the Russian Elections Committee of the place of the meeting five days before it takes place.
Next Tuesday is the deadline for candidates not nominated by a political party represented in parliament to submit their applications, meaning that today is the last possible day to register the meeting.
Mr Kasparov said venues he and his supporters had booked had called back to cancel the booking. He said he suspected the authorities of trying to stop him from registering. He leads the United Civil Front, part of the oppositionist Other Russia movement.
Analysts say the first deputy prime minister Dmitry Medvedev is almost certain to win the elections. He received Vladimir Putin's backing on Monday.