Angry protesters again took to the streets in Ferguson, Missouri, late Sunday, following the shooting death of an unarmed black teenager by a white police officer.
Television footage showed heavily armed police officers apparently firing tear gas at the protesters who tried marching toward them.
The police are preparing to enforce a curfew for the second straight night. The curfew begins at midnight local time and runs until 5 a.m.
Speaking at a rally in Ferguson attended by hundreds of people, including the victim's parents, civil rghts leader Rev. Al Sharpton called the teenagers shooting by a white police officer a "defining moment" for the United States.
Meanwhile, the federal government announced on Sunday that it will conduct a separate autopsy in the shooting of 18-year-old Michael Brown on August 9.
The incident set off daily protests in Ferguson as well as rallies in other parts the country.
According to the U.S. Department of Justice, results from the federal and state autopsies will be considered during the investigation of the shooting.
"Due to the extraordinary circumstances involved in this case and at the request of the Brown family, Attorney General Holder has instructed Justice Department officials to arrange for an additional autopsy to be performed by a federal medical examiner," agency spokesman Brian Fallon said in a written statement on Sunday.
Seven people were arrested early Sunday as police used smoke and tear gas to enforce a curfew in Ferguson.
Missouri state police say they responded strongly Sunday out of fear for officers' safety. Police say one person was critically injured in a shooting nearby that appeared unrelated to the protests.
On Sunday, Missouri Governor Jay Nixon said the five-hour curfew in Ferguson, imposed on Saturday after several days of protests following the shooting death of Brown a week ago, had helped maintain peace.
Asked on CNN's program on Sunday how long the curfew in the St. Louis suburb would continue, Nixon said the duration would be “judged by the community.”
Nixon also said on Sunday that he appreciates the parallel investigation into the police shooting death that is being conducted by the U.S. Justice Department.
“I think that having the dual investigations will guarantee that it gets done in a timely fashion, that it's done thoroughly and that it gets justice,” Nixon said.
Earlier Sunday, scores of demonstrators had remained in the streets after the curfew took effect.
Law enforcement officials used loudspeakers to warn protesters to disperse immediately. Officers, equipped with gas masks and full-length shields, stood among and on top of armored vehicles.
Nixon said Saturday the state of emergency was not to silence people but to contain a handful of looters who are endangering the community.
Missouri State Highway Patrol Captain Ron Johnson, who was named by the governor this week to oversee security in the town, said protesters weren't the reason for the escalated police reaction early Sunday morning.
Johnson said they responded strongly Sunday out of fear for officers' safety.
Johnson said canisters of smoke and later tear gas were fired as part of police attempts to reach the victim of a shooting at a restaurant, “and not in relation to the curfew.”
The person shot at a restaurant during the night was in critical condition, Johnson said. Police were unable to identify the victim, whom Johnson said was not shot by police.
The wounded person was taken to hospital by bystanders before police could reach him.
Johnson also said someone had shot at a passing police car but was not apprehended.
He said a city curfew will run each night from midnight until 5 a.m. until further notice.
The governor told CNN on Sunday tensions in Ferguson were likely to remain high, citing the community response as "raw and appropriate."
Brown's family and supporters have demanded for days that the officer who shot Brown be held accountable.
The U.S. Department of Justice is investigating the shooting for any civil rights violations, and the St. Louis County Police department is also investigating the shooting.
For days, police repeatedly refused to identify the officer involved, citing concerns for his safety. On Friday, Ferguson Police Chief Tom Jackson gave in to community pressure and identified Darren Wilson, 28, as the officer involved.
But at the same time, Jackson added to the community's outrage when he announced Brown had been a suspect in the robbery of a convenience store at the time he was shot.