By Hilary Russ

NEW YORK, April 30 (Reuters) - New York Mayor Bill de Blasio denied that the city had toughened its policing strategy in response to the riots in Baltimore after some lawmakers accused the city's police force of overly aggressive tactics in its handling of protests on Wednesday night.

During a series of marches across Manhattan to protest the death of Freddie Gray, a black man who suffered severe spinal injuries while in police custody in Baltimore, there were 143 arrests, mainly for obstructing traffic. Riots in Baltimore after Gray's funeral on Monday led to arson and looting, as well as injuries to about 20 police officers.

"The strategic approach is exactly the same," de Blasio told a news conference. "We won't tolerate illegality, we won't tolerate disorder. We will not allow the few to undermine the honest efforts of the many to express their views."

Some lawmakers had a different view.

"It was overly aggressive," said New York State Assemblyman Michael Blake, who participated in Wednesday's protests, which started from Union Square.

"Most officers acted responsibly. However, there were too many unjust, incredibly inexcusable acts by officers last night without explanation," he said in a phone interview.

Priscilla Gonzalez, a spokeswoman for Communities United for Police Reform, said in a statement it is "unacceptable that Mayor de Blasio refused to take responsibility for the systemic lack of respect that the NYPD showed for the rights of peaceful protesters."

Last year, New York City Police Commissioner Bill Bratton was criticized for allowing groups of protesters to disrupt traffic by marching down the middle of major thoroughfares without getting a permit beforehand. Those protests were about the deaths of Eric Garner on Staten Island and Michael Brown in Ferguson, Missouri, who both died at the hands of police.

Speaking at a press event, James O'Neill, the Chief of Department of the NYPD, said that officers used tough tactics on Wednesday only in response to the crowd - when they defied orders to stay out of the streets or resisted arrest - but that there was no directive to crack down harder on protests in the wake of violence in Baltimore.

"Throughout the night we were extremely flexible, and we will continue to be flexible," said Police Commissioner William Bratton at the same event. "Our response often times is dictated by the circumstances."

De Blasio said the police approached incidents on a case-by-case basis and that run-ins were a result of a handful of protesters who were either intent on violence or disobeyed police orders.