Several people were arrested Tuesday after hundreds of protesters began demonstrations at New York's Union Square to condemn police brutality across the country, according to reports. Two police officers were also attacked during the protests in the city's Brooklyn borough and police are looking for suspects.

Traffic on the Brooklyn Bridge was partially blocked by the protesters while people on the Brooklyn side reportedly blocked inbound traffic for half an hour. About 34 people had been arrested by 6:40 p.m., and the number of arrests was expected to increase overnight, the New York Times reported, citing NYPD spokesman Stephen Davis. While one officer was reportedly hit in the face while getting out of a police car, another was injured by a bottle thrown at his head, CBS New York reported. 

“Any other person who might use the right to peaceful protest as cover to initiate violence, cause mayhem or incite disorder — whether against the police, the people or property of our great city — should consider themselves on notice that New York City will not stand for it,” New York Mayor Bill de Blasio said, according to the Times, adding that violence against officers was not acceptable.

However, protesters claimed that some officers had shown excessive force. “I got my wrist smashed into,” Bob Lindgren of Brooklyn, said, according to CBS New York, adding: “They threw some guy into a wall.”

The country has seen a spate of incidents over the past year, where police officers have been accused of using excessive force while making arrests, often resulting in the death of those being apprehended. The protests are being organized by a group called “National Actions to Stop Murder By Police,” which claims that over 90 unarmed people have been killed by police officers across the country since the beginning of 2015. 

"The point is that business as usual in this country includes police murdering people and getting away with it," Carl Dix, one of the protest organizers, said, according to WABC-TV New York, adding:  "And business as usual has got to be stopped."

Protesters highlighted the deaths of New York’s Eric Garner, Michael Brown in Missouri and Walter Scott in South Carolina, and carried banners announcing, “Stop murder by police.”

The demonstrations are being witnessed in over 30 cities in 18 states. In Chicago, about 200 people gathered at Daley Center Plaza to protest against the use of excessive force by police officers. Five people were arrested in the city for blocking traffic during the protests, according to the Chicago Sun Times.

Demonstrations were also witnessed in Seattle where people blocked traffic near the Westlake Park for over an hour. In downtown Los Angeles, about 15 protesters were arrested after they disobeyed a police order to disperse, ABC7 Los Angeles reported. Nearly 100 protesters had also gathered outside the Los Angeles Police Department. In Oakland, California, protesters tried to block Interstate 880 before officers cleared the area. Six protesters on the Bay Bridge were reportedly arrested.