A Minneapolis police officer was killed in an ambush when he responded to a call of a double shooting at an apartment building and began giving medical aid to a man who appeared to be a victim, but who turned and fired on the officer, according to reports.

Jamal Mitchell, 36, who had been on the force for less than two years, died in an exchange of gunfire Thursday, the Associated Press reported.

"I've seen the video, and he was ambushed," Minnesota Bureau of Criminal Apprehension Superintendent Drew Evans said at a news conference Thursday evening. "I'm using the term for a reason."

Minneapolis Mayor Jacob Frey called Mitchell a "courageous hero."

"Today, he made the ultimate sacrifice to protect and save the lives of others. His life, his service and his name will forever be remembered in the City of Minneapolis," Frey said. "Our hearts go out to Officer Mitchell's family and loved ones, to the families of the victims of this senseless tragedy and to the members of our extraordinary police department who are grieving."

Mitchell, a father and fiancé who had been honored on his third day on the job for rescuing a couple from a house fire, was responding to calls about a double shooting at an apartment building, the AP reported. 

As he neared the scene, Mitchell noticed two people who appeared to be injured and got out of his cruiser to help them. 

One of the men shot Mitchell. 

Another officer exchanged gunfire with the shooter, who was killed despite lifesaving efforts, the police department said.

The police officer received non-life-threatening injuries. Another person, believed to be a bystander, was injured, as was a firefighter. 

When officers reached the apartment, they found two people who had been shot. One was dead and the other was taken to a local hospital in critical condition. The mayor cautioned that the investigation is continuing. 

He asked people to "be patient with us as we do not know all the facts yet. We want to make sure that the investigation is completed and that we're doing it the right way."

Mitchell was the first officer fatally shot in the line of duty in more than 20 years.