The U.S. Army, which has struggled in recent years to combat a mounting suicide toll, took an unusual step when it announced Wednesday that it had charged eight American soldiers serving in Afghanistan in connection with the apparent suicide of one of their lower-ranking comrades.

The charges in the death of Pvt. Danny Chen, a 19-year-old infantryman from New York City, came after a vigorous, weeks-long campaign by advocacy groups and family members hoping to pressure the Pentagon to investigate allegations that Chen had been the subject of hazing within the ranks and had been repeatedly taunted with racial slurs.

On Oct. 3, Chen was found dead in a guard tower at a small combat outpost in Kandahar province. He was killed by an “apparent self-inflicted gunshot wound,” according to a statement by the NATO command in southern Afghanistan.

Although the exact circumstances of his death are unclear, advocates speaking for his family said Wednesday that regardless of who fired the bullet that killed Chen, the soldiers who allegedly mistreated him are responsible.

“Whether suicide or not, the actions of these people led to his death, and they must be prosecuted for killing him,” said Liz Ou­Yang, a Chinese American activist who pushed for an investigation of Chen’s death. “There can be no plea-bargaining — they must be tried in the death of Danny Chen.”

After more than two months of agonizing over the family’s loss, “it’s of some comfort and relief to learn that the Army is taking this seriously,” said Chen’s mother, Su Zhen Chen, in a Manhattan news conference organized by OuYang. Speaking through an interpreter, she said she hopes that “the truth will come out and that what happened will not be repeated.”

The soldier’s father, Yen Tao Chen, said the military’s action “gives us some hope.”

Military officials declined Wednesday to release documents detailing the charges against the soldiers and did not give an account of the events that led to Chen’s death. But a spokesman for the Army’s Criminal Investigation Command said the probe into how Chen died includes “the circumstances leading up to his death.”

The Army said 1st Lt. Daniel J. Schwartz, Staff Sgt. Blaine G. Dugas, Staff Sgt. Andrew J. Van Bockel, Sgt. Adam M. Holcomb, Sgt. Jeffrey T. Hurst, Spec. Thomas P. Curtis, Spec. Ryan J. Offutt and Sgt. Travis F. Carden had been charged with counts that include dereliction of duty, making a false statement, assault, negligent homicide and reckless endangerment.

Reached Wednesday, some family members of the accused said they were shocked to hear of the charges.

Sheila Dugas, the mother of Blaine Dugas, said the allegations are “completely out of character” for her son. “He was always just taking care of his boys, his troops.”

Bretta Von Bockel, hearing the news about the accusations against her brother for the first time, said she could not believe it. “We worry about him every day,” she said.

Rarely have service members been charged in connection with a comrade’s suicide. If Chen did take his own life, he would be the second Asian American known to have done so this year after apparently being mistreated by his comrades. Marine Lance Cpl. Harry Lew, 21, shot himself April 3 after being hazed the night before by fellow service members, the Marine Corps Times reported.

One of Lew’s comrades was charged with cruelty and maltreatment, the newspaper reported.

The Army’s efforts to reduce suicides include a monthly meeting in which Gen. Peter Chiarelli, the service’s vice chief of staff, speaks with officials from all of the Army’s major bases to review cases. But there has been no sea change in the suicide rate.

Through the end of November, the Army reported 154 possible suicides of active-duty service members this year, slightly ahead of last year’s pace; 159 active-duty soldiers took their own lives in 2010. The number of suicides in the Army Reserve and National Guard has fallen significantly this year.

OuYang, the president of the New York chapter of OCA, an Asian American advocacy group, said that the case “could have easily been swept under the rug” had OCA not pushed the Pentagon to act. Three weeks after Chen was found dead, she sent a letter to the secretary of the Army asking for a meeting to discuss the case as well as concerns that Asian American soldiers face discrimination from comrades.

“The community, elected officials and the media demanded the truth,” she said. “That all played an important role in obtaining justice in this case.”

Chen and the eight defendants were assigned to C Company, 3rd Battalion, 21st Infantry Regiment, based at Fort Wainwright, Alaska. Sgt. 1st Class Alan G. Davis, a military spokesman, said the accused have been transferred from their post in Kandahar to a different military base and relieved of their official duties. He said they are under “increased supervision” but are not being detained. Davis said they will probably be prosecuted in Afghanistan.

Van Bockel, Halcomb, Hurst, Curtis and Offutt were charged with involuntary manslaughter, assault consummated by battery, negligent homicide and reckless endangerment, according to the statement by the NATO command.

Schwartz, the only officer among the defendants, was charged with dereliction of duty. Dugas was charged with dereliction of duty and making a false statement. Carden was charged with assault and maltreatment.

Chen’s death and the reports that he had been mistreated incensed Asian American activists in New York, who called on the military to carry out a swift investigation. Hundreds attended a vigil in Manhattan last week to demand answers.

OuYang said Chen, who was born in the United States, had been subjected to ethnic slurs and physical abuse by superiors shortly before he died. Referring to an account that military officials provided to the Chen family, she said the physical abuse left marks on his back. Fellow soldiers once forced Chen out of bed and dragged him across the floor to punish him for failing to turn off a water heater, OuYang said. The alleged mistreatment was reported by the New York Times on Oct. 30.

Chen, the son of immigrants who live in New York’s Chinatown and speak little English, indicated to his parents that he was being bullied but also told them that such treatment was “to be expected,” the Times report said.

OuYang said Chen’s diaries and e-mails show a pattern of harassment that began at Fort Benning, Ga., during basic training this year. “He was taunted several days,” she said. “Some of it was ignorance, some of it was outright taunting.”

Reached Wednesday afternoon by phone, Chen’s mother said: “We are always missing our son. That’s what’s on our minds.”

Davenport reported from Washington. Staff researcher Jennifer Jenkins and staff writers Greg Jaffe, Debbi Wilgoren and Doris Truong contributed to this report.