Ivan Sekretarev/AP Photo

Tens of thousands of protesters took to the streets Moscow on Sunday, the eve of President-elect Vladimir Putin's inauguration, in the largest and most confrontational protest since December.

By the end of the day,  hundreds were arrested during bitter clashes between protesters and riot police.

Russian news reports estimated the crowd size was at least 20,000 people.

Police said there were 8,000 people there.

One leader told ABC News she believed up to 70,000 turned out, and others put the number even higher than that. They chanted "Russia without Putin" and "Putin is a thief."

Thousands of police were on hand as well.

Police say 250 were detained, opposition figures say more than 400. Putin's spokesman was quoted saying he wishes police had been rougher in their response.

The march began peacefully with a festive atmosphere.

A marching band led the way as a who's who of protest leaders walked towards a stage where they planned to give speeches.

Plans for a rally, however, never materialized as protest leaders staged a sit-in halfway through the march and confronted riot police, who eventually moved in and arrested them.

When the rest of the crowd defied orders to vacate the square when the rally permit expired, riot police linked arms and cleared protestors out of the square by force, at times using tear gas to disperse them. As they did the crowd shouted their disapproval, chanting "Shame, shame, shame."

Some in the crowd threw rocks and bottles. According to some reports some ripped the helmets off of the riot police and tossed them in the river.

Police then began arresting people in greater numbers.

In effect, this is what organizers had in mind. One protest leader told ABC News they wanted pictures of arrests to color press coverage of Putin's inauguration on Monday.

But not everyone in the crowd was happy. One woman who said she didn't approve of the confrontational methods used by protest leaders Sunday.

She said she felt misled into turning out for a rally that never happened.

Before the protest Sunday many wondered whether the protest movement had lost its momentum amid falling turnouts for previous protests and internal divisions among the leadership about how best to proceed.

Sunday's tactics will no doubt fuel the debate about how best to keep up the pressure going forward, as the opposition looks to see how it will affect Putin, if at all.

According to Interfax, authorities say police acted professionally, adding that 27 policemen were injured during Sunday's operation, including three who were hospitalized. They said some suffered from stab wounds and other injuries.

There are also reports that a van for the pro-Kremlin station NTV was set upon by protesters who attempted to flip it over.