MADISON, Wis. -- A 19-year-old black man who died after being shot by a white police officer was unarmed, the Madison police chief said Saturday, assuring protesters who earlier in the day had chanted "Black Lives Matter" that his department would defend their rights to gather while imploring the community to express their anger with "responsibility and restraint."

Tony Robinson was shot Friday night after assaulting Officer Matt Kenny, Madison Police Chief Mike Koval said. Kenny was injured, Koval said, but didn't provide details. It wasn't clear whether Robinson, who died at a hospital, was alone in the apartment.

"He was unarmed. That's going to make this all the more complicated for the investigators, for the public to accept," Koval said during a news conference. Police department spokesman Joel DeSpain said Kenny would not have been wearing a body camera.

Several dozen protesters gathered earlier Saturday outside of the Dane County Public Safety Building holding signs that read "Black Lives Matter" -- a slogan adopted by activists and protesters around the U.S. after recent officer-involved deaths of unarmed blacks -- before walking toward the neighbourhood where the shooting took place. Protesters also shouted the slogan Friday night.

Koval, who struck a conciliatory tone during Saturday's news conference, said he understood the anger and distrust taking hold in the community and that "for those who do want to take to the street and protest," his department would be there to "defend, facilitate, foster those First Amendment rights of assembly and freedom of speech."

He also asked protesters to follow what he said was the lead of Robinson's family in asking for "nondestructive" demonstrations.

Kenny has more than 12 years of experience, Koval said, and was involved in a 2007 shooting but was cleared of any wrongdoing because it was a "suicide by cop-type" situation. He has been placed on administrative leave pending the results of this investigation by the state's Division of Criminal Investigation and the Dane County District Attorney's review of that investigation.

A 2014 Wisconsin law requires police departments to have outside agencies probe officer-involved deaths after three high-profile incidents within a decade -- including one in Madison -- didn't result in criminal charges, raising questions from the victims' families about the integrity of the nvestigations.

State Attorney General Brad Schimel said the department will not share details of the investigation until it is finished. "We are resolved that the result of that investigation will be one in which the public can have confidence," he added.

The shooting came days after the U.S. Justice Department cleared Darren Wilson, the white former Ferguson, Missouri, officer who shot and killed 18-year-old Michael Brown, who was black and unarmed, of federal civil rights charges. A second report found patterns of racial profiling, bigotry and profit-driven law enforcement and court practices in the St. Louis suburb.

There have been several high-profile deaths of black suspects killed by police officers in recent months. In New York City, Eric Garner died after officers put him in a chokehold and a video showed him repeatedly saying, "I can't breathe." A police officer in Cleveland fatally shot 12-year-old Tamir Rice, who had been pointing a pellet gun at a playground. And although Milwaukee police determined the officer who fatally shot Dontre Hamilton acted in self-defence, he was fired for ignoring department policy and treating Hamilton as a criminal by frisking him.

Madison, about 80 miles (130 kilometres) west of Milwaukee, is the state capital and home to the University of Wisconsin's flagship campus. About 7 per cent of the city's 243,000 residents are black.

Koval said police responded to a call about 6:30 p.m. Friday of a person jumping into traffic. A second call to police said the man was "responsible for a battery," Koval said.

Kenny went to an apartment and forced his way inside after hearing a disturbance. Koval said the officer was assaulted by Robinson, and then fired at him.

Late Saturday afternoon, people filled the Fountain of Life Covenant Church for a community meeting. Family members took the stage and read a statement prepared by Robinson's mother, Andrea Irwin.

"I can't even compute what has happened," Irwin's statement said. "I haven't even had a chance to see his body."

She was not present, and the statement said she was taking time to grieve with her children. Robinson's grandmother, Sharon Irwin, was on the stage as the statement was read, but left immediately after.

Koval, who said he went to Robinson's mother's house overnight and spoke with the 19-year-old's grandparents, expressed his sympathy Saturday, saying, "19 years old is too young."