NEW YORK - Thousands of demonstrators have taken to the streets in the U.S. to raise their voices against what they say is corporate excess. But after police in riot helmets swept them from their original encampment this week, Occupy Wall Street protesters are singling out officers as another enemy, saying their crowd control tactics were an excessive use of force against free speech.

"Police Brutality," protesters' signs blared Thursday, in a day of protests across the country to mark the two-month mark of the Occupy movement.

New York officials have called for investigations of the police raid of Zuccotti Park in lower Manhattan early Tuesday.

"The police played their role. I wouldn't call it respectful," said Danny Shaw, 33, on Thursday.

The image of an 84-year-old woman who was tear-gassed in the face in Oakland, California, and hundreds of arrests of demonstrators and journalists at protests across the U.S. this week shone the spotlight on the crowd control tactics of police who broke up encampments in New York and other cities.

Experts on policing say departments have used necessary tactics to control unpredictable, sometimes violent protesters, and that the police haven't yet reached the stages of full riot protection.

"I don't think they're rioting at Occupy Wall Street, not yet, but they are getting out of control," said Maki Haberfeld, a professor of police studies at John Jay College of Criminal Justice in New York. "If they were rioting, you would see much more riot gear" like sonic devices and high-powered weapons, she said.

"When somebody puts their hands on somebody itself, it never looks right," Haberfeld said. "But this is what they're allowed to do. ... It is truly not excessive, and I am surprised by how not excessive it is."

The demonstrations Thursday -- in such cities as Los Angeles, Boston, Las Vegas, Washington and Portland, Ore. -- were for the most part peaceful. But at least 300 people were arrested in New York and dozens were arrested elsewhere, including five on charges they assaulted police officers by throwing liquid into several officers' faces and tossing glass at another.

"We will assure that everyone has the right to exercise their First Amendment rights," New York Mayor Michael Bloomberg said Thursday after visiting one hospitalized officer who needed 20 stitches on his hand. But "if anyone's actions cross the line and threaten the health and safety of others including our first responders, we will respond accordingly."

Chanting "All day, all week, shut down Wall Street," more than 1,000 protesters gathered near the New York Stock Exchange and sat down in several intersections. Several thousand jammed Manhattan's Foley Square Thursday evening and marched to the Brooklyn Bridge.

Several weeks ago, an attempt to march across the bridge drew the first significant international attention to the Occupy movement as more than 700 people were arrested.

In Seattle, hundreds of Occupy Seattle and labour demonstrators shut down the University Bridge.

In Los Angeles, helmeted police equipped with batons surrounded the base of a bank tower, but the protest remained peaceful as several hundred Occupy sympathizers marched. Police arrested two dozen people after they sat down in a street.

Police arrested 21 demonstrators in Las Vegas, and 20 were led away in plastic handcuffs in Portland, Oregon, for sitting down on a bridge. At least a dozen were arrested in St. Louis after they sat down cross-legged and locked arms in an attempt to block a bridge over the Mississippi River.

Several of the demonstrations coincided with an event planned months earlier by a coalition of unions and liberal groups, including Moveon.org and the Service Employees International Union, in which out-of-work people walked over bridges in several cities to protest high unemployment.

The street demonstrations also marked two months since the Occupy movement sprang to life in New York on Sept. 17. They were planned well before police raided a number of encampments in U.S. cities over the past few days, but were seen by some activists as a way to demonstrate their resolve in the wake of the crackdown.

Live television shots Thursday showed waves of police and protesters shoving back metal barricades set up to separate the protest from the public in downtown Manhattan. Some of the police hit protesters as they resisted arrest.

Emmanuel Pardilla, 20, said the heavy police presence "added to the fear tactic."

First Amendment experts said that every interaction with demonstrators, particularly when televised nationally, can thwart the goal of protests and discourage others from joining.

"That's really is terribly inhibiting," said New York attorney Herald Fahringer. "Because people say, 'Gee, well, I don't want to go out there and join the protest if I run the risk of getting hit over the head with a billy club."