Amid calls for an independent investigation into the police-involved shooting of a troubled teenager in Brooklyn Monday, Commissioner Raymond Kelly yesterday stood by the actions of his officers.

From behind a podium at One Police Plaza, Mr. Kelly asserted that the five police officers that fired 20 bullets at 18-year-old Khiel Coppin were left with no choice.

Coppin, 18, was shot in front of his home in the Bedford-Stuyvesant section of Brooklyn at 7:18 p.m. after he pointed what officers believed was a gun, Mr. Kelly said. Police later found a black hairbrush beneath his body, he said.

As news spread about the fatal shooting yesterday, the fragile relationship between police and a Bedford-Stuyvesant community comprising mainly African Americans, became quickly apparent.

Protestors gathered in front of Coppin’s home at 590 Gates Ave. before marching to the 79th precinct. Several demonstrators said the shooting brought back memories of Sean Bell, an unarmed man who was killed by police in a flurry of 50 gunshots last November in Queens.

“Our boys are dying in the streets, its no time for calm,” a protestor, Calvin Hunt, said. “You can’t think you can just come and gun us down. We’ll be here every day.”

The events described by Mr. Kelly leading up to the shooting painted a morose picture of the victim, who he said spent time in a mental institution and at the time of his death was carrying four notes alluding to suicide.

Fearing for Coppin’s well being, his mother, Denise Owens, had called a mobile crisis unit from the Interfaith Medical Center at about 12 p.m. on the day of the shooting, Mr. Kelly said. Coppin was not at home when specialists arrived at 6 p.m.

Mrs. Owens said she threatened to call 911 twice during the day to “scare” Coppin, and finally did so at 7:05 p.m., Mr. Kelly said.

As a frantic Mrs. Owens called for police, Coppin can be heard five times in the background of the recording boasting that he had a gun. During a follow-up call placed to Mrs. Owens, she told a 911 operator that Coppin was unarmed.

Two police officers arrived at the scene at 7:07 p.m., and as they walked through an open door into the family’s first-floor apartment, Coppin lunged at them with two knives, Mr. Kelly said.

The police retreated from the apartment, and called for emergency service units, who are trained at dealing with the mentally disturbed, Mr. Kelly said.

Coppin continuously taunted the officers from a bedroom in the apartment, telling them he had a gun, Mr. Kelly said. At 7:18 p.m., just as emergency units were arriving, he climbed out of a window, and began walking toward police on the street outside of the building, Mr. Kelly said.

Ignoring multiple demands to drop to the ground, Coppin confronted police, who had taken cover behind a patrol car. When Coppin had moved within seven feet of the officers, he stuck his right hand into the bottom of his black sweatshirt, pulling the hairbrush and pointing it at police, Mr. Kelly said.

Two sergeants, a detective, and two police officers opened fire, shooting Coppin 10 times, Mr. Kelly said. He was later pronounced dead at Woodhull Hospital.

Representatives from the community did not immediately agree with Mr. Kelly’s assertion that the shooting was justified. The lawyer for Coppin’s family, Paul Wooten, and representatives from the Reverend Al Sharpton’s National Action Network and from 100 Blacks In Law Enforcement Who Care called for an investigation into the shooting.