AP Photo/Ivan Sekretarev

Opponents of Russian President-elect Vladimir Putin are planning to hold another large protest in central Moscow Sunday, the eve of his inauguration.

The plan calls for protesters to march down a main avenue to a rally on an island in the middle of the Moscow river across from the Kremlin.

Organizers have called it the "March of Millions," though they concede privately that they expect about 25,000 people to turn out.

According to organizers and reports on social media, several activists have been prevented from traveling to Moscow to attend the rally, including some who were removed from trains or stopped along the road and held for questioning.

Some protest leaders say they will try to occupy a square near the Kremlin in the hopes of drawing more attention both within Russia and abroad. Russian news reports say thousands of police have been deployed to prevent exactly that.

The protest comes at a critical moment for the budding opposition movement.

After drawing more than 100,000 people to protests in December, only about 20,000 people attended rallies after the election. Opposition leaders say they are at a crossroad as they struggle to maintain momentum in a movement that appeared to shake Putin's stranglehold on power just months ago.

Thousands took to the streets after parliamentary elections in December kept Putin's United Russia party in power amid allegations of massive fraud. Anger had been building ever since Putin announced plans in September to swap places with his protégé, President Dmitri Medvedev, and return to the Kremlin for a third term.

Ultimately, however, Putin retained significant support in rural areas and won every region except for Moscow in the March 4 elections.

After Putin's victory divisions within the oppositions have only grown amid waning support and questions about how best to keep up the pressure.

Some more radical elements have advocated for civil disobedience and have been repeatedly arrested by police after defying restrictions on rally permits. Others have argued they must shift attention to local and regional elections outside of the major cities, trying to build support where Putin's support remains strongest.

The movement has always been fragmented, an awkward alliance between factions that have little in common other than their opposition to Putin.

Liberals and environmental activists shared the stage with right-wing nationalists, often cringing when amid chants of "Putin is a thief," they shouted slogans praising the glory of Russia.

Many organizers privately worry that they lost their opportunity to keep up the pressure on Putin before the elections, leaving many to wonder what they could have done better. Most agree, however, that Sunday's protest will be critical to keeping up the pressure on Putin going forward.

Opposition leaders are also anxious to see how Putin will respond. Russian authorities appeared to tolerate protests before the election, but have not hesitated to detain protestor who defied the end of permitted protests since then.

One organizer, Natalia Pelevine, says she hopes to be arrested at Sunday's protest.

"I want images of our arrest playing during his inauguration tomorrow," she said.

Some opposition leaders are also planning another silent protest on Monday as Putin's motorcade makes its way to the Kremlin for the inauguration. They plan to hold white ribbons, the symbol of the opposition, along a major avenue on Putin's route into the city.

The hacker group Anonymous has also planned to target Putin's inauguration, saying in a message posted on YouTube on Friday that they will attempt to bring down several Russian government websites on Monday.