(FOX NEWS) -- More than 2,000 law enforcement officers were injured in the first weeks of protests over the summer following the police killing of George Floyd, according to a report released in October.

The Major Cities Chiefs Association, a professional association comprised of local law enforcement heads from the 69 largest police agencies in the United States and nine in Canada, detailed the unrest and compiled data from protests between May 25 and July 31 in MCCA member cities.

During that period, there were 8,700 protests nationwide; 574 were declared riots with violence and other criminal acts. The violence was limited to 7% of protests, the report said.

More than half of demonstrations were peaceful and lawful while other periods of unrest stretched law enforcement at times, the MCCA said.

In most cases, the criminal acts were the work of individuals or small groups that infiltrated larger demonstrations, according to the organization.

"Nonetheless, the sheer volume of protests, combined with the level of civil disobedience and existence of some ultra-violent events, created an extraordinarily challenging environment for law enforcement agencies," the MCCA stated.

The report is primarily based on law enforcement accounts of the protests from each jurisdiction. The largest numbers of protests occurred in New York City and Los Angeles County, with each having over 1,000 gatherings.

Houston had the largest crowd for a single event with 60,000 protesters.

There was violence in more than 62% of Portland, Ore., demonstrations. The city had weeks of nightly protests far beyond the July 31 cutoff for the MCAA report.

At some gatherings nationwide there was looting, violent clashes between protesters and authorities, arson, murder and shootings. Around 72% of law enforcement agencies reported officers harmed during protests.

In total, more than 624 arsons were reported and 97 police vehicles were burned, the report states. Video of some of the protests posted to social media showed officers pelted with bricks, water bottles, fireworks and other objects, including Molotov cocktails.

"One agency reported dumpsters, trash cans, trees, furniture and vehicles being set on fire," the report said. "In many cities, city hall, as well as other iconic public buildings and federal courthouses were targets of arson."

Looting was also common, with 2,385 incidents reported in the 10-week period. While officers were targeted in some cases, authorities in several cities also were criticized for what some saw as an aggressive response to peaceful gatherings.

Many of the non-violent, illegal acts committed during the events were often the blocking of freeways, protesters disrupting outdoor dining, harassing patrons and trespassing onto private property. More than 40% of all protests involved some civil disobedience, the report said.

Over the 10 weeks cited by the report, more than 16,200 people were arrested for protest-related crimes. More than half of the law enforcement agencies said local district attorneys declined to prosecute those cases.

"In some instances, prosecutors refused to charge those arrested for felony crimes committed during the protests despite the availability of video evidence and suspect confessions," the report said.

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