A total of 23 protesters were arrested Friday outside the "Urban Shield" event, the nation's largest first-responder exercise, at the Alameda County Fairgrounds in Pleasanton, a spokesman for the protesters said.

The 23 were cited and released from the Santa Rita Jail at about 1:10 p.m. after being arrested outside the fairgrounds at 4501 Pleasanton Ave. in Pleasanton, spokesman Mohamed Shehk with Critical Resistance said.

The arrests were made for trespassing and obstructing a road. None of the protesters were injured.

Some of those arrested had locked their arms inside pipes outside some of the gates to the fairgrounds, Shehk said.

The protesters started gathering outside the event at about 7:30 a.m. and by about 8:20 a.m. about 400 were at the fairgrounds.

Portions of Bernal, Valley and Pleasanton avenues were closed because of the protests, but the roads were all reported as open just before 1 p.m. Friday, according to Pleasanton police.

One of the claims of protesters was that police are becoming more militarized, adopting military weaponry such as riot gear and armored vehicles.

But sheriff's spokesman Sgt. J.D. Nelson said first responders have been adopting military equipment for the last 100 years such as bulletproof vests.

"It's all military technology," Nelson said.

But Shehk said the equipment is used to repress people, especially people of color and poor people. They are tools of surveillance and control, he said.

The protesters are standing for people who want self-determination. Protesters planned to have speakers, performances and a march. The group was expecting as many as 1,000 demonstrators, Shehk said.

Shehk claimed that police raids have increased to 80,000 per year from 3,000 a year in the 1980s and the raids occur for less serious offenses than they did in the 1980s.

"We see police are inherently violent and inherently oppressive," he said.

Nelson said Urban Shield aims to help first responders prepare to natural and manmade disasters.

He said some people say police don't do enough and others protest police work.

Last year, about 150 people protested the Urban Shield conference by gathering in front of the Alameda County Sheriff's Office near Lake Merritt in Oakland.

Last year was the first year the conference moved to the fairgrounds in Pleasanton from Oakland after city officials decided not to pursue a contract with Urban Shield for 2015. Previous conferences were held in Oakland.

Urban Shield is in its 10th year, Nelson said. Friday, vendors will show off equipment. Also, first responders will receive a safety briefing and medical assessment in preparation for a 48-hour exercise this weekend.

Nelson said every 60 days there is a mass killing in the U.S. and Urban Shield is meant to train first responders for those killings. He said first responders from Boston were grateful for the training they received, which prepared them to respond to the 2013 Boston Marathon bombing.